Dr. Robert Cialdini defined social proof as people doing what they observe other people doing. It’s a principle that’s based upon the idea of safety in numbers. Social proof plays off our insecurities and desire to do the “right thing.”
Occasionally, in studies, users state that they don’t care about user reviews, they don’t trust other people’s opinions, and they make all of their decisions based totally on their own independent perspective. Unfortunately, thousands of psychology studies prove this statement false — another example of why we should base design decisions on what users do rather than what they say.
Several websites use this to make sure that a viewer is converted to a customer. Take Amazon for example, before purchasing a product, its reviews and star ratings are considered by the customer. If the product has been reviewed favourably, especially by a certified buyer then it must be good. To ensure sales, Amazon also has ‘customer who viewed this also viewed’ section. It tells the viewer that if people like him who viewed the product have viewed the others in the aforesaid section then there must be a cause and he should too.