Explain your knowledge to test your understanding and prevent overconfidence

Make a list of five topics you have strong views about
These are also likely to be topics you believe you know well.

To gauge your knowledge, try to explain one of the subjects to a friend
If no one is available, stand in front of a mirror and explain the subject to yourself. Do you notice gaps in your knowledge? Are you starting to doubt your conclusions? Is your position becoming less extreme?

Look into the information you are missing and consider the viability of alternative views
This search may lead to new discoveries and reinforce how much there is to learn.

Repeat this exercise for the next topic, and work your way down the list
You may be surprised by how much or how little you actually know.