Unfortunately, far too many people take advice like that LITERALLY.

The bitcoin address that you get if you use "correct horse battery staple" as a "brainwallet" (calculate the SHA256 hash of the phrase and use the result as a Bitcoin Private key) is 1JwSSubhmg6iPtRjtyqhUYYH7bZg3Lfy1T and there have been more than 15.9 BTC sent to that address in the past 6 years. Some of those were small value at the time and probably sent as a joke.  Some were larger value and almost certainly were sent by a fool and quickly taken by someone else.