Requiring that passwords conform to rules of length, complexity, and unpredictability increases the likelihood of someone gaining unauthorized access to a user' s account  Since most user accounts are automatically locked after a certain number of incorrect password guesses, it is usually impossible to gain access by guessing a password
However, because complex passwords can be hard to remember, users often write them down
People who use mnemonic devices to help remember their passwords are able to easily remember passwords that are long, complex, and unpredictable.