There are a lot of axioms that get tossed around in creative writing courses, books on writing, and of course, the Internet. Often, these little gems are explained to new writers as though they were fact, to be taken for granted.
Just as often, experienced writers will respond by saying "there are no hard and fast rules when it comes to writing", or "rules are made to be broken".
So, the purpose of this question is to provide a place where we can list these axioms or "rules" of writing, and also weigh in on whether they are really self-evident truths or utter garbage (or maybe even something in-between).
Please limit each answer to a single "rule" and express your thoughts on it in the answer itself, or in a comment.