This rule is relevant when we smile because teeth are one of the first points of reference when meeting and talking to people. More and more, because of the lives we lead, we are forced to draw conclusions about people from what we see of them. A smile in one of these situation can convey a huge amount of information. After all, it is by no accident that we have oversized flat front teeth. They have a dual purpose, being both physically functional for eating but also, and most importantly in this matter, for display. Most of us respond very strongly to this built-in display mechanism, which shows itself most often in the form of a smile. Immediately when we see a smile we respond without consciously thinking about it using this 7/10 rule. Some deep primeval instinct genetically imprinted in us quietly advises us according to what we see.