As with so many other things, it only takes one. Guessing your password is the proverbial foot in the door. Once on a system it is easier for an intruder to compromise other accounts, use the system's resources to cause more trouble elsewhere, or bring the system down entirely. They'd never guess that. And if we know it, so do other people.
Exotic words are still words.
I'll use a word from a foreign language. More are being created every day. Don't tell your password to anyone, even if they claim to be a system administrator. Under no circumstances does a system administrator need your password. If you receive mail asking you to change your password to something specific, don't.