The way you tell a story can make your younger self sound more certain than they were.

Telling smooths things out. The version you narrate has you deciding, knowing, choosing, because a story needs an agent, and the person who was actually there was mostly confused and improvising. Repeat it enough and the confident version replaces your access to how uncertain it felt.

When you tell a formative story, try including the part where you did not know. It is truer and it is more useful to whoever is listening, especially if they are currently in the confused stage of something. Certainty is almost always added afterwards.