I can tell you about my own path to running, although I'm not sure it will serve as much as a model for anyone else.

I was initially interested in running for exercise for two reasons. First, because it's very efficient—you can get all the aerobic exercise you need for a day in just 20 minutes or so. Second, because I wanted the capability—I figured sometimes it's handy to be able to run, and the only way to develop and maintain that capability is to run.

What I didn't know was that running would be fun.

Except—and this is key—running isn't fun at the start. Running only starts to be fun when you get pretty good at it. Until you can run for 30 or 40 minutes—a level of fitness that might take weeks or months to achieve, if you're in poor condition to start with—running is no fun at all.

When I first started running, I couldn't run a quarter of a mile. I spent weeks during which I'd run as far as I could—for 5, 6, 7, minutes—and then just walk until I'd gone a mile or so. Gradually, the fraction of the route that I'd run grew and I didn't have to walk as much.

Then, about the time I could run for 12 minutes, I discovered that I'd turned a corner. Once I could run for 12 minutes, I could run 20 minutes. Until then, my heart and lungs couldn't quite keep up—I'd build up an oxygen deficit each minute, until I had to slow down. But at some point—and for me it was when I could run 12 minutes—my cardiovascular capacity provided what I needed to run. It quit being the limiting factor. After that, the limiting factor was my legs instead. I didn't get out of breath, but my legs got tired and sore.

Until then, running was mostly just drudgery. The only reason I was able to stick with it, was that it only took a few minutes, after which I figured I'd gotten all the exercise that I needed to get.

After that, and especially starting just a few weeks later, as my legs got stronger, I suddenly started to really enjoy the runs. I started being able to get some variety—some days I'd run further than usual, other days I'd run faster than usual. I started being able to run other places—after work, in the neighborhood of the office, or on a trail at a park.

That's when I started loving running—when I got in good enough shape that it didn't require that I make a maximum effort every time I went out for a run.

Oh, and I think the endocannabinoids played a part as well.