Good luck remembering what you put there when asked 10 years later.

Yeah, many do not even allow you to enter in a custom question, which would be marginally better--at least for users who care about security.

Then you'd have the option to craft a question which is (A) personally memorable (B) specifically phrased to avoid ambiguity, (C) not public or guessable, and (D) unique to a service.

* "Where is your first pet buried?"

* "While on vacation, The Noodle Incident happened in which city?"

* In what year did you first see Example Band live in concert along with Alice and Bob?"