If you still act on your confidence, but learn to give the right answers understating it in conversation, it could be that you gave those same right answers on the test reactively and then their interpretation is probably flawed.
In this case, additional knowledge wouldn’t actually represent a diminishment of your confidence in a functional sense, but a learned compensation to social feedback.
What does that mean? If you're overconfident in the forest and nobody hears it, it doesn't really matter, right?