When you tell someone that you’re a runner, they’re probably not going to say that they’d like to be a runner too. Even though this isn’t always true for short distances, telling someone that you ran a marathon sends everyone but other marathoners and proud masochists reeling in confusion. To 99 percent of the public, saying you ran a marathon is like saying you walked across broken glass: certainly impressive but something they’d never want to do. When I crossed the finish line of my first marathon last Saturday, I was overwhelmed by the feeling that I had accomplished a rare feat, one that almost no one even considers.

My passion for running has turned me into a gangly scarecrow subsisting on Clif bars, so I understand the people who argue that it’s a demanding and meaningless sport. It took me over two years of vomiting, cramping and finishing last in every race before I started to think of running as more than a chore. I was nine years old then. For anyone to stick with something they hate for that long doesn’t make sense. Running is neither a social sport nor an easy one, and it necessitates many hours in lonely pain that many people would find more punishing than rewarding.

For all these reasons and more, runners make up a select few athletes, and marathoners are only a fraction of those few. In a sense, this is what adds appeal to marathons for the people who do them. Putting it like that might make marathon running look like an ego-driven venture, but the catch-22 is that having an ego isn’t conducive to finishing the race. While many runners might try to encourage people to try marathons by saying they aren’t that hard, I’m here to confess that running a marathon is unbelievably hard.

If you’re aiming for a specific time, it’s necessary to micromanage every second of the race. Knowing exactly when and how much to push yourself, how many sips of water to drink and at which mile you tend to slow down requires mental engagement and months of practice, both of which deter anyone from doing it just to say they did it. These concerns can sometimes apply to shorter races, but in a marathon, they make the difference between finishing strong and being hospitalized.

I’ve been trying for years to find a convincing response to people who ask why I run. The only answer I came up with dawned on me during the last mile of the race, when I knew I would finish in three hours flat. The epiphany came as a quote from Slaughterhouse-Five, when the protagonist, who is writing an anti-war book, grapples with a question from a friend: “‘Why don’t you write an anti-glacier book instead?’ What he meant, of course, was that there would always be wars, that they were as easy to stop as glaciers.”

In 2015, it’s common knowledge that glaciers are melting and have been for decades. I can’t be sure if Kurt Vonnegut knew this when he wrote Slaughterhouse-Five in the 1960s, but the fact that glaciers are receding radically changes the meaning of the quote. To approach marathons with the infallible belief that they’re impossible makes them into a glacier that the mind can only look at and say, “I can’t.” For those who don’t run marathons, they will continue to look as unstoppable as glaciers. For those who do, crossing the finish is as powerful as watching one form.