I think I suffer mostly out of habit having been trained in a pavlovian way through childhood sports. I also find that I'm suffering a lot and nearly all the time whether I choose to suffer or not, so I prefer to allocate that suffering to something that might yield a reward while distracting me from my emotional background noise.

I suffer somewhat pathologically. Sometimes I do it with no more purpose than I have when picking off a scab. I do it because I'm curious about what grows back. I do it because I'd rather be full of scars of my own making. I do it because I'm curious about what's left and what happens when I can't suffer anymore. I do it because if I can suffer more than most people there's some place in the world for me.

I don't know how much suffering is right, what kinds are real, what yield to expect, or where it should sprout from. But, when I'm looking for suffering, I look for something to pursue that I'm very interested in that has a low probability of reward in a future so distant it might not come. I look for a tall metaphorical mountain, situated in my favorite biome without a visible peak, and I climb it.