[pdpi]

> Otherwise you're just skipping out on the stuff that will make you a better/stronger person in favor of some outcome that doesn't truly matter in the long term.

This is the tricky bit. The stated goal is "running a marathon". What you're effectively saying is that the stated goal is not the real goal, and that the real goal is self-improvement for its own sake, with the marathon just being an arbitrary OKR.

Perhaps I'm already in a perfectly fine physical condition, I'm more than capable of running a marathon, and all the preparation I need is learning the pace of a marathon. Perhaps all those self-improvement benefits are things I've already achieved in my life and are not lessons I need to relearn. Perhaps I don't give a damn about any of those so-called self-improvement benefits, and just want to run.

What I "should" get from the experience is entirely up to me, and you're in no position to impose more goals than the stated "I want to run a marathon" goal.