COVER YOUR LEFT EYE, put your face close to the screen, and look at the X. As you slowly pull your face away from the screen, at some point the 0 will disappear. Or cover your right eye and look at the 0, and pull away, and the X will disappear.

You have a blind spot in each eye where the bundles of nerve fibers go back into your brain. But notice something: You don’t see the blind spot. It doesn’t show up like a dark, empty spot. Your brain fills in the emptiness.

In a similar way, when there is information you don’t know, your brain fills it in, giving you the feeling that nothing is missing. In other words, when you feel certain, it doesn’t really mean much. Your feeling of certainty doesn’t necessarily have any relationship to your actual correctness or knowledge. Your brain produces a feeling of certainty at the drop of a hat because it’s wired up to do so.

All human brains tend to jump to conclusions and then feel certain about those conclusions, so it pays to be somewhat skeptical of your own mind. That may seem like a negative goal, but it isn’t. Feeling certain has caused more problems for people than skepticism ever did.

For example, when you’re arguing with your spouse, the thing that keeps the anger intense is that you’re both certain you’re right. If each of you had a little more skepticism about your own ability to remember and reason, it would be easier to work out your differences.

To take another example, depressed people would get depressed less often if they became more skeptical of the pessimistic assumptions they make. The feeling of certainty depressed people have about their own pessimistic view of the world does them harm.

Don’t place much importance in your feelings of certainty. Be skeptical. Recognize you have blind spots and act accordingly. You’ll be saner if you do.