The author describes the main subject of his book as "thin-slicing": our ability to use limited information from a very narrow period of experience to come to a conclusion. This idea suggests that spontaneous decisions are often as good as—or even better than—carefully planned and considered ones. To reinforce his ideas, Gladwell draws from a wide range of examples from science and medicine (including malpractice suits), sales and advertising, gambling, speed dating (and predicting divorce), tennis, military war games, and the movies and popular music. Gladwell also uses many examples of regular people's experiences with "thin-slicing," including our instinctive ability to mind-read, which is how we can get to know a person's emotions just by looking at his or her face.
Gladwell explains how an expert's ability to "thin slice" can be corrupted by their likes and dislikes, prejudices, and stereotypes (even unconscious ones). Two particular forms of unconscious bias Gladwell discusses are implicit association tests and psychological priming.
Gladwell also mentions that sometimes having too much information can interfere with the accuracy of a judgment, or a doctor's diagnosis. In what Gladwell contends is an age of information overload, he finds that experts often make better decisions with snap judgments than they do with volumes of analysis. This is commonly called "Analysis paralysis." The challenge is to sift through and focus on only the most critical information. The other information may be irrelevant and confusing. Collecting more information, in most cases, may reinforce our judgment but does not help make it more accurate. Gladwell explains that better judgments can be executed from simplicity and frugality of information. If the big picture is clear enough to decide, then decide from this without using a magnifying glass.
The book argues that intuitive judgment is developed by experience, training, and knowledge. For example, Gladwell claims that prejudice can operate at an intuitive unconscious level, even in individuals whose conscious attitudes are not prejudiced. An example is in the halo effect, where a person having a salient positive quality is thought to be superior in other, unrelated respects. Gladwell uses the 1999 killing of Amadou Diallo, where four New York policemen shot an innocent man on his doorstep 41 times, as another example of how rapid, intuitive judgment can have disastrous effects.