Essentially, we have two different thought systems that work very differently, and Kahneman refers to them throughout the book as characters he calls System 1 and System 2. System 1 is a marvel honed by millions of years of evolution that runs on automatic (and can’t be turned off). It’s a virtuoso at jumping to (usually correct) conclusions on the basis of very little information. A master at coming up with shortcuts (heuristics) that usually work, we couldn’t get through a minute of our day without it. As Kahneman points out, most of what we know about System 1 would have “seemed like science fiction” 30 or 40 years ago. Unfortunately, System 1 can’t be reflective. It can’t know what it doesn’t know, but it always knows that it’s right. And because it works so much faster and more smoothly than System 2, it almost always overrules our more rational selves.
System 2 is generally clueless about System 1’s flaws. It’s too slow and inefficient to handle immediate matters; it consumes huge amounts of energy, takes effort and time, and requires a great deal of self-control. Since “laziness is built deep into our nature,” we mostly glide along on System 1. System 2 is supposed to be the overseer, the skeptic, the doubter, but it’s often busy and tired and defers to System 1, which is gullible and biased. In fact, System 2 is often an apologist for System 1. “Its search for information and arguments is mostly constrained to information that is consistent with existing beliefs,” Kahneman explains.