Social proof is a psychological phenomenon where people assume the actions of others in an attempt to reflect correct behavior for a given situation. It is used in ambiguous social situations where people are unable to determine the appropriate mode of behavior, and is driven by the assumption that the surrounding people possess more knowledge about the current situation. Social proof is one type of conformity, and it is used in marketing to influence the purchase decisions of prospective and returning customers.

There are six types of social proof: expert, celebrity, user, the wisdom of the crowd, friends, and certification. Brands leverage social proof as a way to increase conversions and grow their customer base exponentially as more people join in and create buzz around products or services. Social proof is also one of Robert Cialdinis six principles of persuasion, which maintains that people are especially likely to perform certain actions if they can.

Social proof is more powerful when being accurate is more important and when others are perceived as especially knowledgeable. Social proof often leads not only to public compliance (conforming to the behavior of others publicly without necessarily believing it is correct) but also private acceptance (conforming out of a genuine belief that others are correct).

In summary, social proof is a psychological concept where people copy the actions of others in choosing how to behave in a given situation. It is used in marketing to influence the purchase decisions of prospective and returning customers. There are six types of social proof, and it is more powerful when being accurate is more important and when others are perceived as especially knowledgeable.