The utmost extent of man’s knowledge, is to know that he knows nothing.

The further into a subject you get, the more clearly you can see the edges of what you have. Confidence peaks early, in the stretch where you know enough to hold opinions and not enough to know what is missing. Recognising your own ignorance is not modesty; it is an achievement that takes considerable knowledge to reach.

When you next feel completely certain, treat that as a prompt to check rather than permission to relax. Ask what would have to be true for you to be wrong. If nothing comes to mind, you are probably early.