Mental Models

Frameworks for thinking about and understanding the world and our impact on it.

Nuclear-Powered Pacemakers

In the mid 20th century, a promising new power source for pacemakers emerged: plutonium-238.

Plutonium is a radioactive material, which meant it could be used in extremely small quantities to create nuclear-powered pacemakers. Since lithium-ion batteries weren't commercially available yet, we had to get creative with our power sources.

By the time the first plutonium-powered pacemaker was implanted in a human in 1970, we knew enough about radiation to understand its dangers and how much exposure was safe. This new generation of devices had no long-term, ill effects on its hosts.

But even though it might technically be safe to walk around with trace amounts of plutonium powering your heart, this is still a terrible idea, and there are two groups that really, really hated it.

The first is the Nuclear Regulatory Commission, which likes to keep track of where radioactive material is stored. Surgically implanting plutonium inside of people before sending them back out into the world makes that difficult.

And the second group that hated nuclear-powered pacemakers?

The crematorium industry.

You see, when you heat a pacemaker up to 1,500° fahrenheit, it has a nasty tendency to explode, causing non-trivial damage.

This phenomenon — pacemaker explosions in crematoria — is actually not exclusive to plutonium-powered pacemakers, since batteries behave similarly at extreme temperatures. In fact, as recently as 2002, researchers Christopher P. Gale and Graham P. Mulley found that roughly half of the UK's crematoria have experienced pacemaker explosions. They write in their paper's abstract:

We found [. . .] that pacemaker explosions may cause structural damage and injury and that most crematoria staff are unaware of the explosive potential of implantable cardiac defibrillators.

You might be wondering, "how is this possible?" Surely there must be a process in place for preventing this kind of thing from happening. And you'd be correct. Gale and Mulley have an answer:

Crematoria staff rely on the accurate completion of cremation forms, and doctors who sign cremation forms have a legal obligation to provide such information.

Of course, even doctors make mistakes sometimes, and things slip through the cracks.

Most of us are fortunate to not have to make life or death decisions in our work. You may not be in a position where a wrong decision leads to serious injury, but when creating something new or changing an existing process, it's still worth asking: What could go wrong? And when something does go wrong, despite your preventative measures, how do you plan for that?

Coincidentally, the same year doctors implanted the first nuclear pacemaker in a human, William Haddon created the Haddon Matrix, the most commonly used framework in the injury prevention field for evaluating risk factors before, during, and after an incident.

Here's an example Haddon matrix from Wikipedia:

Table displaying example Haddon Matrix

Such a formal risk evaluation might be overkill most of the time, but it's a useful reminder that every decision we make has second-order effects.

When we acknowledge that the world is messy and anticipate that multiple things can — and will — go wrong, we can design around and plan for those events.

And please, whatever you do, don't put plutonium inside of people.

P.S. Here's an image of Brunhilde, the world's first nuclear-powered dog (he received a plutonium pacemaker in 1969). Clearly a good doggo, despite being slightly more radioactive than most pups.

Black and white image of the profile of Brunhilde sitting in grass
Via Nuclear Newswir

Argue the Opposite

Having a strong opinion requires work, because you need to be able to argue your perspective effectively.

The best way to do this? Practice arguing the other side as well. Only then can you truly understand the debate.

Investor Charlie Munger understood this when he said:

I never allow myself to have an opinion on anything that I don’t know the other side’s argument better than they do.

Understanding the other side requires empathy. And when we engage from a place of empathy, we see that our differences often pale in comparison to our similarities.

Convergent vs. Divergent Thinking

Convergent thinking is the practice of solving a problem for which there is only one right answer. It's like a spotlight searching for a target in the dark.

Often, though, there are many right answers, which is where divergent thinking comes in. Like a floodlight illuminating as much of the world as possible, divergent thinking seeks to gather as many answers as possible.

Thomas Edison famously said. “I am quite correctly described as 'more of a sponge than an inventor." He understood that the world is messy, and that by following your curiosity — by practicing divergent thinking — you'd have a better chance of finding the right answer.

So, cast a wide net before trying to converge on a solution. You might just figure out how to make light bulbs technically and commercially viable.

Via The Atlantic. Further reading: "Who really invented the light bulb?" from Science Focus, and the excellent book How We Got to Now by Steven Johnson

Change Your Mind

Politicians are often accused of changing their stances on issues too often. The cynical view is that they're simply trying to pick a collection of beliefs they think will get them the most votes, rather than establishing a consistent ideology.

But the world is changing quickly, and many of us would be better off changing our minds more often to reflect new information.

It's hard to let go of existing beliefs when we use them as the basis for our identity. But changing our mind should be a badge of honor. It doesn't make us look flaky — it shows others that we're capable of growth.

When we let go of preconceived notions, we can see the world more clearly for what it is.

Knowledge Trees

Knowledge resembles a tree.

The core of a subject — the trunk — makes up the foundation of that discipline.

If you're trying to learn cooking, for example, the trunk includes things like basic knife skills, how to measure ingredients, and how to use various heat sources.

After that come the branches. These aren't quite as essential as the trunk, but they're important to learn on your way to mastery.

Things like mise en place, choosing the right kind of pan for each dish, and understanding the chemical reactions that occur during the baking process are branches of the culinary arts.

And lastly we have the leaves. This is the specific knowledge that you'll only use rarely, but is what distinguishes experts from the merely experienced.

In our cooking example, leaf knowledge might include how to extract every ounce of meat from a lobster, techniques for perfect poached eggs, and how the coarseness of different salts affects your meal.

Part of what makes learning something new intimidating is the number of leaves you'll inevitably encounter early on. Without the trunk and branches to mentally hang them off of, you'll struggle to make sense of them.

So start by identifying what the trunk of your topic is. Once you've reached the top off it, figure out the branches that extend out of it. This gives you a sense of what you don't know.

And knowing what you don't know yet is half the battle towards gaining proficiency.

See also: Latticework of Ideas

Systems Thinking

If I could teach my younger self one thing, it would be this: If you’re trying to make a sustainable change in yourself or the world, you need a system for doing so.

The world is a collection of interdependent systems. And when we think holistically about how those systems interact, we’re able to bring about more meaningful change.

On the individual level, if you’re trying to get more exercise, you're more likely to achieve your goal if you block off times a week in advance for each workout, decide what your plan for each one is, and tell a friend you'll buy them dinner every time you miss one.

By creating a specific structure and establishing social support, you can systematically set yourself up for success.

This is true on the societal level as well. When we invest in summer youth employment programs, crime in our communities goes down. And when crime goes down, people are more likely to start businesses in those neighborhoods, which create more jobs. The taxes from that increased economic activity can be reinvested in those summer jobs, and so on.

If this sounds like a flywheel, that's because it is. Ultimately, our ability to create long-term progress boils down to creating the right systems for doing so.

So if there’s already a system in place, but it's not working, make it better. And if there isn’t, make one up.

See also: System Design


A flywheel is essentially a heavy disc capable of holding large amounts of energy. By spinning it faster and faster, you can store your effort to use later.

This has a wide range of industrial applications, like smoothing out the output of an energy source or applying a much stronger, sudden force on something than the energy source could deliver on its own.

Flywheels are so effective, you can even technically use them to power a bus, and in the 1940s, the Swiss did exactly that when they invented the gyrobus. It was just like a normal bus, but instead of running power lines along its entire route or putting a polluting internal combustion engine in it, they added a giant, steel wheel that could be respun at each stop.

Basically, it had a clever, relatively low tech battery.

Unfortunately, running a bus this way is a little impractical. A giant, spinning wheel is energy intensive, changes the physics of turning the vehicle it's inside, and puts passengers near something moving at dangerous speeds.

But flywheels are a useful mental model for thinking about a whole range of things.

A body in motion tends to stay in motion. The challenge is getting it started, because maintaining it is relatively easy, since it requires less energy. If you've ever rolled something heavy, you know how much easier it is to keep it moving than to constantly stop and start.

If you're running a successful business, you can create a flywheel effect by encouraging customers to refer other customers to you through a referral program. This creates sustainable, forward momentum. As you acquire more customers, they tell others, who in turn purchase your product and spread the word as well.

In our personal lives, a flywheel is a metaphor for wellbeing. If you get enough sleep, you're more likely to have the energy and willpower to eat healthy and exercise. This gives you more energy and improves the quality of your sleep.

And so the cycle continues, as long as you keep the wheel spinning.

Car Seats as Contraception

Second-order effects are everywhere.

Researchers Jordan Nickerson and David Solomon, for example, found that US car safety seat laws have resulted in a lower birth rate:

Since 1977, state laws have required children to be restrained by car seats, with the age limits gradually rising over time. The problem for potential parents is that many cars can accommodate two, but not three, car seats in the back row. Car seat laws thus require three-child households to purchase larger cars, indirectly raising the costs of having a third child.

Their paper, Car Seats as Contraception, goes on to suggest that the laws haven't impacted families without a car or with only one child of car seat age.

The effects of this legislation are potentially significant: Nickerson and Solomon estimate 145,000 fewer babies have been born in the U.S. since 1980 as a result.

There are a lot of variables at play in trying to draw a clear cause/effect relationship here. But the broader implication from a study like this — that nothing happens in isolation — is certainly true.

Everything we do is part of a larger system, and it's impossible to change one thing without incurring secondary consequences.

The challenge is thinking far enough ahead to anticipate the full effects of our actions.

See also: Nuclear-Powered Pacemakers

Survivorship Bias

In WWII, aircraft returning from bombing missions often sustained heavy damage from enemy fire. The distribution of holes in the fuselage and wings might look something like this:

Diagram of a plane with red bullet holes
Martin Grandjean (vector), McGeddon (picture), Cameron Moll (concept), CC BY-SA 4.0, via Wikimedia Commons

Imagine you're a WWII-era statistician tasked with assessing the damage of returning airplanes. Which parts of the plane depicted above should you reinforce?

If your answer was the areas with the most bullet holes, you'd be wrong.

Abraham Wald, working with the Statistical Research Group at Columbia University, pointed out that this is a classic example of survivorship bias: Returning aircraft demonstrated where the planes could sustain damage. The additional armor actually needed to go where there weren't bullet holes, because the planes that got hit there never came back.

When we examine our history, it's tempting to look at only the success stories. But the people, societies, and organizations that didn't survive have important stories to tell us as well.

Sometimes, those quiet stories about the ones that didn't succeed have more to tell us than the ones that did.

Opening Doors

When you open a door, if the people following you hold the door open, no one has to go through the effort of opening it again.

This is true for a lot of things. When we put in the effort to solve a problem, we can spare everyone else the hassle by showing our work.

This is why the open source software movement is so important, for example. When a programmer solves a problem and publishes the answer, everyone else gets to freely benefit from it.

Because of this, software development increasingly resembles building with legos. Simply break new problems into a series of smaller problems that have already been solved. By assembling these existing components together, programmers can increase the speed and impact of their work.

The same is true of ideas. When you share a way of looking at the world with others, it opens their eyes to what’s possible. And thanks to the internet, the opportunity to share your ideas with billions of other people is now free.

We’re only just starting to understand the implications of this. But one thing is already clear: The internet enables human potential at scale. By providing access to an unprecedented amount of information and facilitating collaboration, the web enables us to collectively solve ever more sophisticated issues.

The answers to humanity’s greatest problems won’t come from individuals working in isolation. They’ll come from groups of people assembling the building blocks of others’ work into new, innovative solutions.

Let’s keep opening doors for each other.

See also: Abstraction


Reflections on creating systems to sustainably grow your impact on the world.
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