A related issue: the best answer may have a link to the documentation, which may rot. Now people will down-vote the answer because broken link.

This could happen if somebody asks how to do something using some library. If the library actually has a builtin facility to solve the problem, but then the answer gets down-voted due to documentation link rot; then another answer explaining how to built that facility from scratch may become the 'best' answer, even though the re-implementation of existing library functionality is a bad idea.