I’ve worked on other analogies but every simplification is damning in its own way. One I particularly like:

You want to ask Google for directions to an address in your small town but you don’t want Google to know where you are going or where you live. Instead you ask for a list of directions between every address in your small town. It takes a bit longer to return these results but the it satisfies the conditions.

This isn’t of course how ZKP’s work but directionally captures their computational overhead in a way other examples don’t.