Your work becomes legacy when other people can use it without needing your explanation.

Anything that requires you to explain it has not really been handed over. Every use costs someone a conversation with you, which caps how far it can spread and how long it lasts. Legacy begins at the point where the thing carries its own explanation and no longer needs you standing next to it.

Give something you made to a person with no background and watch where they get stuck. Do not help. Their confusion is a precise map of what is still living only in your head.