I'm sure this has been asked and talked about. But this just happened:
I revisited some old question of mine. I noticed a comment and tried to upvote but was told that I already upvoted and cancelled so I can't:
It seems with time I became smarter, so now I know that comment was helpful, but I can't do anything about it.
Same goes for voting for questions - if I change my mind after a while - say I learned something and realised he's right, or of it's in meta say I changed my mind about a topic that doesn't have a right and wrong answer - then I can't change my vote.
I understand why a vote gets "locked". But why can't we allow, say, one change every six months? It's a very specific scenario but customs, technology and opinions change. So maybe that should be allowed.
What do you think?