Related story: For some weird reason, I memorized the serial key for a very popular software (I must be fifteen then). Even today, I can recite the 25-letter key without a hitch. And I have used its first ten letters as a password to one of my accounts. Guess what? The password has been used 4000+ times before [1]. It's hard to digest the fact that there are at least a thousand people in the world who did the same thing.
[1]: https://haveibeenpwned.com/Passwords