Book SummaryThinking in Systems, by Donella H. Meadows

1-Page Summary1-Page Book Summary of Thinking in Systems

Thinking in Systems is an introduction to systems analysis. Many aspects of the world operate as complicated systems, rather than simple cause-effect relationships. Many problems in the world manifest from defects in how the systems work. Understanding how systems work, and how to intervene in them, is key to producing the changes you seek.

What Is a System?

A system is composed of three things:

1. Elements: The individual things in the system
2. Interconnections: The relationships between the elements
3. Purpose or Function: What the system achieves

To define it more cohesively, a system is a set of elements that is interconnected in a way that achieves its function.

Many things in the world operate as systems.

• A football team consists of a group of players on the field, each with a specific role that interacts with the others. The larger team system also consists of coaches, support staff, and fans.
• Within the system of a corporation, people, machines, and information work together to achieve the corporation’s goals. This corporation then takes place within the larger system of the economy.

Stocks and Flows

Stocks and flows are the foundation of every system.

A stock represents the elements in a system that you can see, count or measure. It can be commonly thought of as an inventory, a store, or a backlog.

Flows are the means by which the stocks change over time. Inflows increase the level of stock, while outflows decrease the level of stock.

Let’s take a simple system: a bathtub.

• The stock is the amount of water in the tub.
• The inflow is water coming from the faucet into the tub. This raises the stock.
• The outflow is the drain that removes water from the tub. This decreases the stock.

This can be drawn on a stock-and-flow diagram, as here:

Many systems are analogous to the bathtub:

• In fossil fuels, the stock is the reservoir of fossil fuels. Mining lowers the stock, while natural processes increase the stock.
• The world population is a stock of people. The population grows with births and shrinks with deaths.

Properties of Stocks and Flows

Stocks take time to change. In a bathtub, think about how quick it is to change the inflow or outflow. It takes just a second to turn on the faucet. It takes minutes to fill the tub.

Why do stocks change so gradually? Because it takes time for the flows to flow. As a result, stocks change slowly. They act as buffers, delays, and lags. They are shock absorbers to the system.

From a human point of view, this has both benefits and drawbacks. On one hand, stocks represent stability. They let inflows and outflows go out of balance for a period of time.

• Your bank account stores money and gives your life stability. If you get fired from your job, the inflow of money will stop, but you can take money from your stock to continue living and figure out how to solve the problem.

On the other hand, a slowly-changing stock means things can’t change overnight.

• If a population’s skills become meaningless because of technology, you can’t re-educate the workforce instantaneously. It takes time for the information to work its way through the system and to flow to the population.

Where We Focus

As humans, when we look at systems, we tend to focus more on stocks than on flows. Furthermore, we tend to focus more on inflows than on outflows.

• When thinking about how the world population is growing, we naturally think about how increasing births must be driving the trend. We think less about how preventing death through better medical care also grows the population.
• Likewise, a company that wants to increase its headcount does so instinctively by hiring more people. It doesn’t often think as hard about how to reduce the outflow of people who quit or are fired.

This is just one example of how we, as simplicity-seeking humans, tend to ignore the complexity of systems and thus develop incomplete understandings of how to intervene.

Feedback Loops

Systems often produce behaviors that are persistent over time. In one type of case, the system seems self-correcting—stocks stay around a certain level. In another case, the system seems to spiral out of control—it either rockets up exponentially, or it shrinks very quickly.

When a behavior is persistent like this, it’s likely governed by a feedback loop. Loops form when changes in a stock affect the flows of the stock.

Balancing Feedback Loops (Stabilizing)

Also known as: negative feedback loops or self-regulation.

In balancing feedback loops, there is an acceptable setpoint of stock. If the stock changes relative to this acceptable level, the flows change to push it back to the acceptable level.

• If the stock dips below this level, the inflows increase and the outflows decrease, to increase the stock level.
• If the stock rises above the acceptable level, the inflows decrease and the outflows increase, to decrease the stock level.

An intuitive example is keeping a bathtub water level steady.

• If the level is too low, plug the drain and turn on the faucet.
• If the level is too high and the water spills out of the tub, open the drain and turn off the faucet.

Reinforcing Feedback Loops (Runaway)

Also known as: positive feedback loops, vicious cycles, virtuous cycles, flywheel effects, snowballing, compound growth, or exponential growth.

Reinforcing feedback loops have the opposite effect of balancing feedback loops—they amplify the change in stock and cause it to grow more quickly or shrink more quickly.

• As a stock level increases, the inflow also increases (or the outflow decreases), causing the stock level to further rise.
• In the other direction, as a stock level decreases, the inflow also decreases (or the outflow...

Thinking in Systems Summary Introduction: Seeing Things as Systems

What is a system? A system is 1) a group of things that 2) interact to 3) produce a pattern of behavior.

Many things in the world operate as systems.

• The human liver is a group of cells that interact to detoxify the blood, among other functions. The liver is, in turn, part of the larger system of the human body.
• A football team consists of a group of players on the field, each with a specific role that interacts with the others. The team also consists of coaches, support staff, and fans.
• Within the system of a corporation, people, machines, and information work together to achieve the corporation’s goals. This corporation then takes place within the larger system of the economy.

Systems may look different on the surface, but if they have the same underlying structure, they tend to behave similarly.

• For example, consider the simple system of a bathtub. There is a spout that adds water to the system, and a drain that removes water from the system. If the spout adds water faster than it drains, the bathtub will fill and the water level will rise. Conversely, if the drain removes water faster than the spout adds water, the bathtub will empty.
• Now...

Thinking in Systems Summary Part 1: What Are Systems? | Chapter 1: Definitions

A system is composed of three things:

1. Elements: The individual things in the system
2. Interconnections: The relationships between the elements
3. Purpose or Function: What the system achieves

To define it more cohesively, a system is a set of elements that is interconnected in a way that achieves its function.

Many things in ordinary life are systems. Let’s define how a professional football team is a system:

• Elements: The players, the coaches, the field of play, the ball
• Interconnections: The rules of football, the way players in specific roles interact with each other, how the coaches instruct the players, how the laws of physics govern how the ball moves
• Purpose: To win football games, to have fun, to make money

As you look around the world, you’ll see systems everywhere. So what is not a system? A set of elements that are not interconnected in a meaningful way or overall function is not a system. For example, a pile of gravel that happens to be on a road is not a system—it’s not interconnected with other elements and does not serve a discernible purpose.

In this chapter, we’ll dive deeper into understanding the three attributes of a...

Shortform Exercise: Define a System

Pick a system that you want to understand better. If you can’t think of one, here are suggestions: your employer; your favorite store; your political party; an organism.

What are the major elements of the system?

Thinking in Systems Summary Chapter 1-2: System Behavior

Next, we’ll understand how systems behave over time, by considering stocks and flows. This forms the basic foundation that lets us build up into more complex systems.

Stocks and Flows

A stock represents the elements in a system that you can see, count or measure. It can be commonly thought of as an inventory, a store, or a backlog.

Flows are the means by which the stocks change over time. Inflows increase the level of stock, while outflows decrease the level of stock.

Let’s take a simple system: a bathtub.

• The stock is the amount of water in the tub.
• The inflow is water coming from the faucet into the tub. This raises the stock.
• The outflow is the drain that removes water from the tub. This decreases the stock.

This can be drawn on a stock-and-flow diagram, as here:

The clouds signify wherever the inflow comes from, and wherever the outflow goes to. To simplify our understanding of a system, we draw boundaries for what’s important for understanding the system, and ignore much of the outside world.

Many systems are analogous to the...

Shortform Exercise: Feedback Loops

Think about everyday systems and how feedback loops affect them.

Can you think of any decision you make where a feedback loop is not involved? What is it?

Thinking in Systems Summary Chapter 2-1: Building More Complicated Systems

In reality, systems are much more complex than the simple examples we’ve covered so far.

• A single stock may not just have an inflow and outflow, but really have multiple flows in and out, as well as multiple balancing and reinforcing loops working in opposite directions.
• A single flow may affect dozens of stocks.
• Feedback loops affect each other, reinforcing each other or balancing each other.

For example, the world population has an inflow representing birth rate, but birth rate is influenced by a vast number of inputs, such as the overall economy, healthcare, and politics, which are themselves complex systems.

In this chapter, we’ll take what we’ve learned and build up to more complicated systems, which are simplistic models of real-world systems. The author calls this collection of systems a “zoo,” which is an appropriate metaphor. Like in a zoo, these animals are removed from their natural complex ecosystem and put in an artificially simplistic environment for observation. But they give a hint of patterns in the real world and yield surprisingly insightful lessons.

One Stock + Two Balancing Loops

First, we’ll look at a system with one stock and two...

Thinking in Systems Summary Chapter 2-2: Two-Stock Systems

So far we’ve just focused on one-stock systems. In the models, we haven’t worried too much about where the inputs came from and how much there were—the population model assumes infinite food, the thermostat model assumes infinite gas to the furnace.

But in the real world, the inputs have to come from somewhere. In a system model, the inflow into a stock comes from another stock, which is finite. This finite stock causes a constraint on growth—the population can’t grow forever, and the economy can’t grow forever.

We’ll explore this here with two system models, one with a non-renewable stock (oil mining) and one with a renewable stock (commercial fishing). Changing whether the stock is renewable changes the implications of how growth ends.

Renewable Stock and a Non-Renewable Stock

Consider a reservoir of oil underground. The stock of oil is finite. There is an outflow as the oil is mined. (Shortform note: There is also a very slow inflow of generation of fossil fuels through geological processes, but this occurs over millions of years and is so slow that it’s irrelevant in this situation.)

The company that decides to mine this oil reservoir is a system. The system looks a...

Thinking in Systems Summary Part 2: Understanding Systems | Chapter 3: Why Systems Perform Well

Systems are capable of accomplishing their purposes remarkably well. They can persist for long periods without any particular oversight, and they can survive changes in the environment remarkably well. Why is that?

Strong systems have three properties:

• Resilience: the ability to bounce back after being stressed
• Self-organization: the ability to make itself more complex
• Hierarchy: the arrangement of a system into layers of systems and subsystems

We’ll discuss each one in more detail.

Resilience

A resilient system is able to persist after being stressed by a perturbation.

• The human body avoids disease by foreign agents, repairs itself after injury, and survives in a wide range of temperatures and food conditions.
• An economy can work its way out of a grave unexpected event and out of recessions.

Think of resilience as the range of conditions in which a system can perform normally. The wider the range of conditions, the more resilient the system.

Resilience doesn’t mean that the behavior is static or a flat line. Dynamic systems, like the year-long oscillation of a tree growing in spring and shedding leaves in fall, can be resilient as well....

Shortform Exercise: Improve Your System

Think about how to improve your system with the three main reasons they perform well.

What’s a system you care about? If you need ideas, consider your employer, a group you belong to, yourself as an individual, or a physical system.

Thinking in Systems Summary Chapter 4: Why We Don’t Understand Systems

We try to understand systems to predict their behavior and know how best to change them. However, we’re often surprised by how differently a system behaves than we expected. Systems thinking is counter-intuitive in many ways, even for trained systems thinkers.

At the core of this confusion is our limitation in comprehension. Our brains prefer simplicity and can only handle so much complexity. That prevents us from seeing things as they really are.

This chapter discusses a collection of such limitations. The underlying themes are:

• Our cognitive biases color how we take in information.
• We tend to focus on obvious points, ignoring the more subtle and complex drivers that really matter.
• Systems often behave in ways that we’re not used to, such as changing nonlinearly or inducing delays.

Limitation #1: Focusing on Events

When we try to understand systems, we tend to see them as a series of events.

• History is presented as a series of factual events, such as presidential elections, wars, and treaties.
• The news reports on stock market movements with great earnestness.

While events are entertaining, they’re not useful for understanding the...

Thinking in Systems Summary Chapter 5: How We Fail in Systems

In previous chapters, we’ve explored a range of system models and how they relate to real-life situations, such as restocking a car inventory lot and managing renewable resources. We’ve explored how misbehaving in the system can cause poor system performance, whether that means wild oscillations in restocking the car lot or driving the fish population to extinction. And in the previous chapter, we covered our limitations in comprehending how systems work.

Taken altogether, it’s little surprise that we can design systems that completely fail to achieve the purpose we desire. Furthermore, when problems appear, we can fail at designing the right solution for the problem, and our behavior can make the situation worse.

In this chapter, we’ll describe system archetypes, which are system structures that produce problematic patterns of behavior (the author also calls them “system traps”). These archetypes are ubiquitous in the real world, explaining phenomena such as nuclear arms races, the war on drugs, and business monopolies. We regularly get mired in these problems, but by understanding how the system predictably produces the behavior, we can also find the right way to...

Thinking in Systems Summary Part 3: Changing Systems | Chapter 6: Twelve Leverage Points

Leverage points are places to intervene in a system. It’s important to 1) find the right leverage point, and 2) push it in the right direction.

Counter-intuitively, people often find a good leverage point, but push it in the wrong direction. Remember the car lot, where reducing delays actually worsened the oscillations.

The author presents 12 leverage points in order of increasing effectiveness.

Shortform Notes on Leverage Points

Before we dive in, some themes to keep in mind:

• Lower leverage points tend to be harder to change or have less influence on the behavior of the system. Changing a system’s flows may do little to change how its feedback loops work.
• In contrast, higher leverage points are so influential that small changes can have vast effects on system behavior. Change a system’s ability to self-organize, and you influence its stocks, flows, and feedback loops.

In addition, at a high level, we group the leverage points into three major categories, also in increasing order of effectiveness:

• The physical system structure: the stocks, flows, and how they connect
• System information and control: how the system regulates itself, such as...

Thinking in Systems Summary Chapter 7: Improving as a System Thinker

Learning to think in systems is a lifelong process. The world is so endlessly complex that there is always something new to learn. Once you think you have a good handle on a system, it behaves in ways that surprise you and require you to revise your model.

And even if you understand a system well and believe you know what should be changed, actually implementing the change is a whole other challenge.

The author ends with advice that she and other systems thinkers have learned over their lifetimes. (Shortform note: We’ve organized her points into three sections:

1. Understanding systems
2. Intervening in systems
3. Systems in society)

Understanding Systems

Before you eagerly dive in and try to repair a system, make sure you understand it well first.

Stop and Watch

We all have our favorite assumptions about how things work, and how problems should be fixed. To truly understand a system, we have to discard these and start from scratch.

To understand a system, first watch to see how it behaves. Get a sense of its beat.

This doesn’t necessarily mean stopping and watching it in real-time. Rather:

• Research its history. How did this system get here?
• Get...