We're blind to our blindness. We have very little idea of how little we know. We're not designed to know how little we know. Most of the time, [trying to judge the validity of our own judgements] is not worth doing. But when the stakes are high, my guess is that asking for the advice of other people is better than criticising yourself, because other people are more likely – if they're intelligent and knowledgeable – to understand your motives and your needs.
From: "Thinking, Fast and Slow" by Daniel Kahneman