Ars Technica:

Diceware is a well-known decades-old system for coming up with passwords. It involves rolling actual six-sided dice as a way to generate truly random numbers that are matched to a long list of English words. Those words are then combined into a non-sensical string (“ample banal bias delta gist latex”) that exhibits true randomness and is therefore difficult to crack. The trick, though, is that these passphrases prove relatively easy for humans to memorize.

It’s like the xkcd about passwords says: the conventional knowledge about ‘hard to hack’ passwords is all wrong.