If you haven’t heard the term ‘Social Proof’ before, don’t worry. Most of us haven’t. That said, if you are in marketing, and you haven’t heard the term ‘Social Proof’ then go bang your head against a wall for a while. Social proof is a simple yet powerful concept. How powerful you ask? Well many great marketers will cite Influence: The Psychology of Persuasion by Robert Cialdini as the most important marketing book ever written. And Cialdini devotes over 50 pages just to social proof.