Why passphrases work
A passphrase strings together several random words. Because it's long, it's very hard for a computer to crack — yet because the words are real, it's far easier for a human to remember than a random jumble of symbols. Four random words drawn from a large word list already give strong protection; five or more is excellent. Passphrases are ideal for the passwords you actually need to type by hand, like your device login or password-manager master password.