Because someone served us directly. Someone took our order, made sure that we had full glasses of ice water, stopped by to see if we needed anything once our order was served, timed the serving of food, fixed the problem if the kitchen made a mistake....that is all direct service to us. That gets a tip.

I tip the manicurist who does my nails for the very same reason. She doesn't pool her tips with those who clean the salon, wash the towels, or refill the lotions. She performs the service of giving manicures; she gets the full tips and she alone.