dholliday
deconstructed rep
The other side of that is that it's far easier to stay a lifelong fan if the worst you've ever had to endure is finishing 3rd.
I think it's not a matter of easy or not. For most of us the club stays forever, regardless. We can't change our mothers either, but we love them so we wouldn't want to.
Saying that, I know of a small handful of more casual fans who have changed clubs (tho' respect to my brother: he was RS as a small boy, but binded himself with the more local Hull City once he got into his teens, and now that seems stuck for life).