Entertaining a notion, like entertaining a baby cousin or entertaining a pack of hyenas, is a dangerous thing to refuse to do.  If you refuse to entertain a baby cousin, the baby cousin may get bored and entertain itself by wandering off and falling down a well.  If you refuse to entertain a pack of hyenas, they may become restless and entertain themselves by devouring you.  But if you refuse to entertain a notion—which is just a fancy way of saying that refuse to think about a certain idea—you have to be much braver than someone who is merely facing some bloodthirsty animals, or some parents who are upset to find their little darling at the bottom of a well, because nobody knows what an idea will do when it goes off to entertain itself, particularly if the idea comes from a sinister villain.

A Series of Unfortunate Events: The Vile Village – Lemony Snicket