You've delved into the work of a whole range of thinkers - psychologists, military leaders, tennis coaches, market researchers - who are exploring a new idea of the unconscious mind. What are they getting at?
The Freudian notion of the unconscious was this weird, murky place where we dealt with emotionally complicated things like sex and violence. The new notion of the unconscious, the adaptive unconscious, has been developed by Timothy D. Wilson at the University of Virginia. He argues that the thing below the surface is like a big computer that crunches data for us. It gathers information from our environment and helps us decide how to prioritize that information. If we had to govern all this consciously, we'd be unable to function.

Among the thinkers you discuss is John Gottman, the University of Washington psychologist who studies marriages. How does his work help us understand snap judgments?
Gottman does what's called "thin-slicing," drawing conclusions based on very narrow slices of experience. He's been doing this since the 1970s with hundreds of couples. Just by watching a 15-minute videotape of a couple interacting, he can predict with almost 90 percent accuracy whether they will still be married 15 years later. He focuses on subtle signs of defensiveness, stonewalling, criticism, and contempt.

So just asking John how he feels about Mary doesn't reveal much about their relationship?
There's an awful lot about who we are that we're not aware of.Think about this: I can't observe my face while I'm talking to you. Maybe my face is communicating that I'm bored or disgusted. I have no idea how you're perceiving me.

One of your main themes is that, thanks to the rapid cognition always going on below the surface, we "know" many things we may be unable to explain.
One of the best examples comes from speed dating, where single men and women have just a few minutes to decide whether they want to date someone. This distills dating to a single snap judgment. For that, you don't need an entire evening, just a thin slice of a few minutes.

You interviewed some Columbia professors who studied speed daters. What did you learn?
When they asked speed daters what they wanted in the opposite sex, and then compared that to what the daters were actually attracted to, the qualities didn't match. A woman would say she wanted a smart, funny guy, then be attracted to someone who wasn't smart and funny. In other words, she starts with a conscious ideal of what she wants, but that's just part of it. The unconscious is working behind a locked door. So our explanations don't always match our behavior.

So can businesses really learn much from the focus groups used to test-market toothpaste, politicians, pop songs - just about everything?
We have all kinds of market research that depends on asking people what they think about a new movie or a detergent. But when you ask people [in focus groups] to explain their first impressions, they often aren't very good at it. They lack the vocabulary for breaking down those snap judgments.

Blink also has much to say about first impressions in hiring. You make the case that gathering more information about a person isn't always helpful; in fact, it can lead us to make mistakes.
A lot of the evidence we gather when we're evaluating someone is irrelevant, but it drowns out things that are relevant. Women couldn't get hired to play in orchestras until they began using blind auditions. Women were said to lack the proper strength or resilience. But when they started [putting players behind screens during auditions], the judges focused only on the music, and their prejudices didn't get in the way.