What is a piece of information that you believed where true, but find out it is mnot?

Well, there is no exact question in musing that is like that but there are similar ones, so i might not deserve to be up-voted, yet I find that my answer would not fit in there question so this is a more broader one.

Anyway for me the first wrong fact I believed or thought was true is the fact that heart beats is produced from the movement of the muscles during beating. they in fact do not, however they are formed from the closure of valves in the heart allowing the blood to leave and go between chambers in the heart.