From a future book by Adam Khan, author of Self-Help Stuff That Works

YOU'VE SEEN OPTICAL ILLUSIONS. They always show up in psychology textbooks. There's a famous one that looks like an old witch or a young lady, depending on how you look at it. There's the simple three dimensional box - look at it one way and it seems you're looking up at it; look at it another way and it seems you're looking down on it. There is a new kind of optical illusion, generated by computers, that give you the impression you're looking into a three dimensional object when your eyes refocus, even though at first it looks like a flat, random pattern.

Psychology students are often introduced to optical illusions, not because most psychology students become eye surgeons, but because the illusions aren't created by our eyes; they're created by our brains. It has nothing to do with your childhood or your personality. Everyone with a normal brain sees the same illusion because it's caused by the way our brains are designed. The specific design of the human brain is very good for some things, and not very good for other things. It is by no means perfect. For example, you've probably seen the optical illusion of the two lines next to each other, one with the arrows pointing out, one with the arrows pointing in.

The lines are the same length, but it doesn't look that way. Even when you know they're the same length - even when you go get a ruler and measure them - they still look like different lengths. What you're experiencing is a flaw in the way your brain perceives.

Our brains are not designed perfectly. We don't perceive perfectly and we don't think with perfect reason. We can call our mistakes in thinking thoughtical illusions.

All human brains tend to make certain mistakes in the same way. In this chapter, we'll explore some of these common mistakes. There is no technique in this chapter. I'm simply trying to show you why it's in your best interest to be sceptical of your own mind. That may seem like a sadistic goal, but it isn't. The feeling of certainty has caused more problems for people than skepticism ever did.

When you're arguing with your spouse, the thing that keeps the anger intense is: 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.

The scientific method has made so much progress because the theories are provisional - good until something better comes along. When a scientist comes up with an idea of how things work, she doesn't call it a Law or a Fact, she calls it a theory. And she fully expects other scientists who come after her to test it and improve it (or trash it if it turns out to be wrong). That attitude allows progress. And it's extremely hard to do. A scientist has to impose the discipline on herself, just as you and I would be wise to do, to prevent herself from thinking of something as a truth.

We have a tendency to come to a conclusion and then close our minds on the matter. Probably for most of our evolutionary history this tendency served us well. Now we are rarely in a life-or-death, you-must-make- a-decision-now situation, and it's usually best to hold off from drawing a conclusion. This has to be done deliberately, however, because your brain just naturally clamps down on the theories you come up with (or get from others) and labels them Facts.

Blind Spots

Cover your left eye and hold your face close to the screen (or the paper if you've printed this out, and look at the X. As you slowly pull 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 I want you to 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 the same way, when there are things 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 anything. Your feeling of certainty often doesn't necessarily have any relationship to your actual correctness or knowledge. Your brain produces that feeling of certainty at the drop of a hat because it's wired up to do so.

This tendency to come to a conclusion quickly and to feel certain about it even when we're wrong is compounded by some other thoughtical illusions. For example, in numerous experiments, researchers have found that our brains automatically seek evidence to confirm (rather than disconfirm) an already existing conclusion - whether we have any personal stake in it or not.

When you allow yourself to come to the conclusion that you aren't very organized, for example, you'll see and remember everything you do that confirms your conclusion even if you don't want it to be true (and ignore the times you were well-organized - because they don't confirm anything; they disconfirm). When you decide your spouse is a slob, you'll notice and remember (clearly) all the times when your spouse acted like a slob, and you'll ignore or explain away all the times when your spouse acts neatly.

Premature conclusions - especially negative conclusions - alter your perception and your reason along those lines. And telling other people makes it even worse.