First off I'd like to say I'm not sure if /r/rpg would be a more appropriate place to bring this up, I've only played pathfinder, so perhaps it could be related to the system. I've been playing pathfinder for just under 2 years now. Since then I've been part of 12 different campaigns, which sounds like a lot, but only 2 of them still happen. They have mostly been adventure paths, with 4 custom games (all the custom games no long run). Two of them have been my own, one of which I'm still running even after having 6 players come and gone, and 2 character retires. I'm wondering if this is normal to never really see the end of campaigns, usually for APs it seems around book 2-3 things die out, and around lvl 8-10 for custom games (granted we only got to lvl 4 in my game).

Is it common to not get all the way though an adventure? I play online with people I know, though many games have "friends of friends", so perhaps that's a factor. What have your experiences been on actually completing stories?