Social proof is a phenomenon in which someone can hardly determine the acceptable behavior to portray and just assumes the behavior portrayed by others. It happens to people that find themselves in unfamiliar setups and thus do not know how to act and have no other reference other than the behaviors observable from other people. This is how people in new setups almost always end up doing what others are doing. In a certain experiment, a group of people was told to look up at the sky in the middle of the city. The end result was catastrophically successful. Other people began staring blindly into space to see what was being looked at. People that observed others doing this also did the same and the ripple effect caused major traffic disruptions as people were looking at the sky in the middle of roads and others from their cars. This was a show of just how powerful social proof is. The act of stopping and staring at the sky for a long duration without looking at anything in particular was quite unfamiliar. Those that found themselves next to people doing this almost immediately started doing the same and the people that observed them also did the same. Social proof is highly used in the fashion industry to push new trends to the market. When people observe a number of people and celebrities wearing some clothes, they also pick them up, and the people that observe people adopting the clothing brands as well go and purchase theirs as well.

Another application of social proof is in entertainment. There are some shows that feature canned laughter where a recording is played of people laughing at presumably humorous sections of the show. However, canned laughter is at times used in rather unfunny sections or at poor jokes and it has the same effect as when used at sections where there are good jokes. Why would someone simply laugh at a dry joke because of canned laughter? The answer is that there is a psychological way of determining correct behavior by inferring to other people and observing to what degree they are doing something. In the same way, people will find something funny if other people find it funny even if it is apparent that their laughter is controlled or manually fixed.

Social proof is an effective influence weapon that gets the best of most people. It is because people like to conform to the behavior observed from other people so as to avoid being peculiar or the odd ones out. In tipping jars, bartenders will place some currency in the jar so that it implies many people have tipped them and to avoid being the stingy ones, other people are more likely to tip them than if the jar was empty. In a rather amusing experiment, participants were put in an elevator in which an unsuspecting subject would get into. After going up a number of floors, the participants would all turn and face a certain direction. The unsuspecting subject would almost always also turn and face the direction the participants turned to. This clearly shows that compliance can be stimulated and this is, therefore, a very dangerous tool in the hands of a social engineer. It can instantly bring out the behavior a social engineer desires in a subject.

For social proof to work, there must exist the following:

• Uncertainty: The target must not have a prior experience of the situation. It must be completely new and ambiguous such that the only way to determine what to do is by looking at what others are doing.
• Similarity: There should be a similar type of reaction by other people. This will show the target that they know what they are doing and the target will have to follow what they do. If there is another confused person, the impact of social proof might not be realized as the two might decide to remain peculiar from the group.

These two conditions can easily be created by social engineers. This is because a social engineer doesn't need not to create a physical situation in order to utilize social proof. Verbally, the social engineer can describe a scenario to make the target appear the only odd one out. The social engineer could say that everyone approached has taken a certain action and it has led to a certain favorable result. The target will be more willing to take the path taken by the others. When entering a premise guarded by a security person, if stopped, a social engineer can just say, I am sorry but yesterday Mat checked my credentials and allowed me in. I figured I was still a welcome visitor. The path presumably taken by Mat will pressure the present guard to allow the social engineer in without rechecking his or her credentials.