It's polite to give warnings.
Jeff manages a grocery store with a dirty floor that needs to be mopped.
Jeff wants to mop the floor throughout the store.
"Jeff puts out ""wet floor"" signs throughout the store and begins his mopping."
"Jeff mops the floor but does not put up a ""wet floor"" sign."
The store's customer's approach cautiously and no one gets hurt.
A customer slips and injures herself.