I have seen on this site questions, mainly by new users, that "forget" to put a reference to a notable claim, and some answers that forget to their credible sources. Those posts get down-votes, as they should. However, I've seen that when those post are fixed, ether by someone else or by the OP. The problem is that many people don't go back to check if the posts they down voted were fixed, which causes good posts to have down-votes from their past.
In order to avoid it, I sometimes go over my down-votes list, to check if posts have been edited or change in a way that fixes them. The problem is that I'm sure that many users don't do it, hence the answers that still have unjustified down votes, Is there a way to make a reminder system, that will encorage people to review their down-votes when an edit has accord to the post.
This is more crucial for questions.
a. because there is a greater chance of an questions to "forget" to put the notable claims, and then fixed.
b. Because there isn't insensitive in the form of regaining lost reputation by un down-voting.