There was a time when I routinely refused car travel, in favor of my more sustainable bicycle. Not always, but I had a high bar—if it was bucketing down with rain and I had no plastic pants, this was not sufficient excuse for instance. I would sometimes decline a ride even when others were purportedly driving somewhere anyway, to avoid encouraging them to be ‘driving anyway’ more often. I did enjoy cycling, on a good day, but many days weren’t good. People at school laughed at me on my bike, so sometimes I walked instead because I couldn’t stand them looking at me. Refusing cars was often a sacrifice.

My concern was the climate. My basic model of ‘sustainability’ was this: humanity has a bunch of resources, and when they run out we all die. If we use them slow enough, they can mostly last forever, but if we use them faster, we will die soon. Much like a bank account that earns lots of interest, or can be spent down in an afternoon. Space in the atmosphere for greenhouse gasses was a key resource. Driving was known to be unsustainable: it added carbon dioxide to the atmosphere faster than could be supported. This model has a few problems I think, but it is debatable, and this blog post is not about them. So lets suppose for now that I was right, and every car trip took humanity a notch closer to annihilation.

Given that driving was unsustainable, I wanted people to stop driving, so we wouldn’t all die. Naturally, it followed that I should not drive (I thought). If the cost of a billion people driving was too great for the benefits of a billion people driving, then the cost of one of those people driving was probably too great for the benefit of that person driving. Furthermore, I seemed a particularly easy person to convince, from my perspective. Furthermore, the benefit of me getting to school sooner and with dry pants was obviously unimaginably minuscule compared to any decrement in humanity’s ability to survive in the long term.

This is all very wrong. Why? Let’s say cycling cost me ten minutes per day (it took more like half an hour per day, but driving also takes time, and cycling had some benefits, such as exercise). If I had spent this 5h per month on writing about the problem, I think I could have convinced more than one person ever to habitually ride a bike. If I had just earned money and given it to an organization specializing in this, they probably could have done better. This is an empirical question, so maybe not, but the problem was that I didn’t even look for such things.

One way to think about this is to say that I was wrong in thinking myself an especially cheap person to change. I might be easy to communicate with and readily convinced (from my perspective). I might be able to get on a bike right now, whereas I had not much idea how to convince anyone else. But I am an extremely expensive person to use the time of (from my perspective), because I am one of the few people who is on board with my schemes and willing to do what I tell myself, and so my own time is one of the few resources that can be spent on the plan of forwarding my values. And given this, there are ways to leverage ten minutes of my time into more than an extra bike ride’s worth of value.

Relatedly, I didn’t compare between options further afield. Even if unsustainable transport was set to destroy the world, and personal action was the cheapest way to get change, it does not follow that I should cycle. For instance, maybe it is even more important to change people’s unsustainable purchasing behavior, and I should have spent that time purchasing things better. Or earning money, and spending it on forwarding sustainability in other ways. Or thinking about how robots might destroy the world more imminently.

More fundamentally, my error was comparing the costs of my sacrifice to what was gained by it, instead of comparing my gains to what I might have had instead. This was both the wrong comparison, and naturally blinded me to the better purchases I might have made. If the question you ask is whether cycling everywhere is worth a tiny fraction of the future, then there is no reason to check how valuable reading about geoengineering is.

So this is what I would tell my younger self. Whether your personal sacrifices are money, time or frustration, you should usually be comparing the benefits of making one personal sacrifice to the benefits of making another. You should not be comparing the personal cost of making a personal sacrifice to the benefits of making that sacrifice. Because what matters is ‘opportunity cost’—the value of the next best option that you are foregoing. And rarely is the next best option to ramp up your leisure budget. Usually the next best option is making a sacrifice for something else overwhelmingly valuable; something measured in units of humanity’s future, or in senseless torment averted. This is true whether you are willing to sacrifice everything for the greater good, or only a tiny bit. Either way, you should spend the sacrifices you make on the best things sacrifices can buy.