The first time I ever ran a marathon was in 2009, while training for the Pittsburgh marathon. I had no training plan, but it felt like I should work up to the real thing before race day. So out I went, running and running. I finished with X laps on a nearby track—in those days I didn't have a GPS tracker or smartphone, so I measured out a course on a map and then padded it a bit to make sure.
When I got back to my house, having accomplished something totally new all by myself, I felt like a total badass. I had to let loose with a wolf hooooowwwl!
Ever since then, every time I finish a course at least marathon length, I do it again, whether it's in training, race, or whatever. (If I'm pacing in a friend, and it's not really my race, I'll refrain, even if I just went 50 miles. It's not my time.)