content: There's over a million words in English.  Lets assume most of them are not useful, and focus on the most common 2000 words (3000 words handles almost every use case).  Join four of them in a random order, and you have 2000^4 = 16 trillion possibilities, and you are VERY CAPABLE of remembering that, because your brain is setup to remember whole words.  The xkcd explains this graphically, with the boxes to each being a bit.    In troubadour, he's giving 16 bits of entropy (65536 possibilities) to the initial uncommon word.  Then he's showing that you add one bit for whether it is capitalized, some extra bits for common substitutions, a bit for whether the trash at the end of the word is in some order, etc.  He comes up with 28 bits.  I think that's about right- he misses several possible things you could do, but his initial guess on word count is pretty damned generous.    Meanwhile, for the correcthorsebatterystaple, he's limiting himself to common words, so each word is only 2048 possibilities (11 bits), but there's four of them.  In practice, it's more than that.    So if you have the word list- the COMPLETE word list of the 2048 possible words- just joining four of them gives you that huge number.    His point- the top thing is susceptible to brute force.  The bottom thing is not.  It is a completely valid point.    But if you want to add some punctuation that you can remember to correcthorsebatterystaple, hey, knock yourself out.  That's fine.  Just don't make your users do it.