Could you imagine if tipping didn't exist and you were the guy tasked with selling the idea to people?
"OK...so let me get this straight... if I go out and pay a restaurant $150 for a couple of steak dinners and a couple of bottles of wine, I should then pay someone an extra $30 on top of that for taking our orders to the kitchen and then carrying that same food 75 feet from our kitchen to the table?"