It is a good idea to have a password written down. You should have told him that it was a /valuable/ piece of paper, that should be kept with other valuable pieces of paper.

Good passwords are hard to remember. Good password discipline uses lots of good passwords. This is harder to remember. Sticking a password file in your wallet is not a bad idea. People know to keep their wallets secure. They understand how they work, and how they need to protect them.