I liked this answer in particular: "These are actually metamathematical (false) beliefs that many intelligent people have while they are learning mathematics,

I liked this answer in particular: "These are actually metamathematical (false) beliefs that many intelligent people have while they are learning mathematics, but usually abandon when their mistake is pointed out, and I am almost certain to draw fire for saying it from those who haven't, together with the reasons for them: * The results must be stated in complete and utter generality. * Easy examples are left as an exercise to the reader. * It is more important to be correct than to be understood. (Applicable to talks as well as papers.)"