Your password must be between eight and sixteen characters.
Your password must contain at least one lower case letter, one upper case letter, one number, and one special character (#, @, or $).
Your password cannot start or end with a number.
Your password contains an invalid character.
You cannot reuse any of your last 24 passwords.
This becomes an even more entertaining game when the web site only tells you the first rule that you have broken.
It very quickly becomes non-trivially difficult to create an easy to remember hard password.