People who know me even slightly, already know I won't shut up about running. This time though, I want to start with a stat from that world before I get to the one that actually stopped me this week.

Running USA's National Runner Survey found that 73% of marathon finishers report a household income over $75,000, against a US median closer to $52,000, and 79% hold a college degree against 27% of the general population. These gaps are large - and it's not so straightforward to explain away, because marathon running is genuinely one of the cheapest ways into competitive sport. A pair of decent shoes and an entry fee will get you to a start line for a few hundred dollars (creeping up these days, but I digress). There's no fancy bike, no equipment arms-race... Nothing close to what other endurance sports can cost. Cost doesn't explain this the way it explains, say, sailing or golf.

A similar story where cost appears as a convincing answer, is Ironman triathlon. Average household income among participants runs close to $240,000 a year, and about a quarter clear $200,000 or more. A race-ready bike costs several thousand dollars on its own, and training eats fifteen to twenty hours a week for the better part of a year. That's a real financial and time commitment, and "no wonder the participants skew towards wealthy" sounds like a complete explanation.

It isn’t though. In both sports, cost only comes close to explaining who “has a crack at it” as we say here in Australia. It doesn't explain who's still on their feet at the end. Plenty of people who can afford the shoes or the bike sign up and get a DNF (did nit finish). I hear the part of an Ironman that does the final sorting isn't the swim or the bike. It's the marathon that is run on legs that have already done 3.8 km of swimming and 180 km of cycling. The same 42.2 km that sorts people on its own, standalone, sorts them again here, but with a lot more fatigue already baked in.

Somewhere in the marathon, everyone has the same conversation with themselves. If I stopped here, nobody is going to know or care. Nobody is chasing you down the course. Nobody calls to check why you didn't finish. The only person enforcing the finish line is you - the person running toward that line. And the ones who win that argument with themselves are the ones who show up in the income and education numbers on the other side.

Outside of income data, there's more research that backs this up. Researchers reviewed multiple studies of marathon runners and found that finishers score higher than the general population on self-sufficiency and energy levels, and lower on fatigue and tension. This has nothing to do with shoes or bikes and everyhting to do with what kind of person keeps moving once your brain has convincingly made the rational case for stopping, Usually somewhere around 30km.

This pattern is not confined to running. Anyone who writes and publishes consistently, week after week, with no editor forcing the deadline, carries it too: most people who start posting on linkedin (😬) quit within a few months, and the habit of not quitting tends to show up later in how they're regarded professionally. Engineers who maintain an open source project for years with no manager assigning the work carry the same thing, and so do people who stick with an instrument long enough to get good at it, past the point where it stops being fun and before it starts being rewarding (Gladwell’s 10,000 hours).

None of these activities cause the career outcome. That distinction matters, because the tempting version of this story is "run a marathon and you'll earn more," and that version is wrong, confusing correlation with causality. What these activities share is the same filter applied in different settings: the willingness to keep going after you've already made a good case to yourself for stopping.

The activity doesn't build that willingness. It just makes it visible.

I think about my own quit points a lot, more than the running ones. The moments in a hard project, a difficult conversation, or a plan that's stopped working, where quitting starts to sound reasonable instead of like failure. Every one of those moments runs the same negotiation in the background: who's going to know or care if I stop here. The people worth building a team around, worth backing, worth spending your days with, are the ones who've had sufficient practice losing that argument to stop taking the bait.

Sources (linked inline, duplicated below):