In the marketplace, social proof is a common way for people to make quick decisions about whether to buy something. For example, many people do not have time to browse through hundreds of books, so they choose one from the bestseller list. They figure that if millions of other people thought a particular book was good, it must be good. Other people do not have time or energy to find out which is the best fax machine or VCR, so they buy whatever model is the hottest seller. A group of tourists walking down a busy street does not know which restaurant has the best food, so they wait in line at the most crowded one they find, thinking that if so many other people are willing to wait, it must be something special.
Social proof provides a shortcut to knowledge that guides our actions.
But social proof is not fool-proof. Sometimes it can lead people astray, and with grave consequences. This is probably what happened to the bystanders in the Kitty Genovese incident. In times of such uncertainty, the natural tendency is to look around at the actions of others for clues. We can learn, from the way the other witnesses are reacting, whether or not the event is an emergency.