“Social proof, a term coined by Robert Cialdini in his 1984 book, Influence, is also known as informational social influence. It describes a psychological and social phenomenon wherein people copy the actions of others in an attempt to undertake behavior in a given situation.” (Wikipedia)
If your friends jumped off a bridge would you jump off too? Psychology says you would. Social Proof is a psychological phenomenon where people assume the actions of others to reflect the right behavior for certain situations.