Mental Models

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

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.

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

Pick Your Compromises

It’s tempting to focus on just the benefits. But every decision comes with trade-offs.

Often, when we get stuck when deciding on something, it helps to invert the problem and consider just the downsides. Doing so makes it easier to approach the issue honestly, because it prevents us from ignoring the downsides we have to accept. It also puts the potential upsides in perspective.

When we pick our compromises this way, we can pursue our path with open eyes and clear intent.


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