All the levers of influence discussed in this book work better under some conditions than others. If we are to defend ourselves adequately against any such lever, it is vital that we know its optimal operating conditions in order to recognize when we are most vulnerable to its influence. In the case of social proof, there are three main optimizing conditions: when we are unsure of what is best to do (uncertainty); when the evidence of what is best to do comes from numerous others (the many); and when that evidence comes from people like us (similarity).
