The most basic motivating force behind social proof is the bandwagon effect, a social psychology concept that states that people are more likely to engage in an action if other people are doing it. For example, if over two million people have purchased a book and enjoyed it, the wisdom of the crowd dictates that you are likely to enjoy the book too.
Another benefit of social proof is that it conveys trust. Trust is one of the key factors in converting customers online, because providing a credit card number to an unknown business over the web is a large hurdle for customers to overcome. Showing potential customers that a business has many satisfied customers through testimonials and user reviews helps build trust that a business is legitimate and trustworthy.
