Nobody humbles you like a younger sibling. Take the free lesson.

Someone who has watched you since you were small is immune to your presentation, because they saw the earlier drafts. They will say the plain thing at the dinner table with no interest in being tactful, and it is often accurate, which is the annoying part. Anyone who cannot be impressed by you is a rare and useful instrument.

Ask one of them what they think about something you have been telling yourself a story about. Take the answer without arguing, even if the delivery is terrible. Sift it afterwards, keep what is true and leave the rest. Free and honest is a combination you will not get often later.