Most of the most important decisions we make, are made in a split second using "thin-slicing" decision making. These decisions are often made more correctly than we can manage if we put our minds to it. For example, doctors diagnosing heart attacks usually go through a long list of tests and procedures to determine if the attack is real. Doctors correctly diagnosed the heart attack 70%-90% of the time. Gladwell cites a study by Dr. Goldman who took hundreds of heart attack case studies into a computer program developed by physicists to build correlation models for particles. The result was a comparatively simple, and much less (needlessly) expensive, algorithm that allowed doctors to correctly diagnose heart attacks more than 95% of the time. Goldman's process, as is the point of the book, happens with less information, much quicker and more accurately than the traditional process.
Interesting tidbit: John Gottman, a psychologist at the University of Washington, has developed a 15 minute analysis, that with a 95% accuracy, can determine if a couple will still be married in 15 years. All by "thin-slicing" the conversation.