I never used to be able to run. When I was at school I'd be breathless and exhausted after one or two laps of the playing field, and I basically never ran if I could avoid it. On the other hand, I enjoyed walking arbitrary distances at speed.
Then a few years ago, on a whim I started running on the beach near my parents' house, and surprised myself by enjoying it. Since then I've often run short distances (a few kilometres). I was curious about what longer distances would be like, but I haven't had the time to try until a couple of times recently: a few months ago I ran 7km in 45 minutes (twice as long as I'd ever run before) and last weekend I ran 17km in two hours. It didn't seem difficult except that my feet got sore, which is perhaps because I was running barefoot: the problem is that if I run in any kind of footwear I own I quickly start feeling tired. There's probably something I could wear that would be OK, but this is part of my larger problem of not knowing anything about running so I'm probably doing it all wrong :-).