Don't bite off more than you can chew; don't start a fight that is too big to win.

an answer of acceptance to an eagerly-awaited question

A polite refusal by someone who has just done a magic trick to reveal how it works. / (by extension) A refusal to explain how one accomplished something impressive.

Alternative form of you're never too old to learn

Synonym of never fight a land war in Asia

Alternative form of a watched pot never boils

Alternative form of you can't judge a book by its cover

Alternative form of the apple does not fall far from the tree

Something is not affected in the same way twice.

(idiomatic) Most things are inherited and predetermined.