It's nice to tip people.
Tom is eating out at a restaurant and has a limited amount of cash on hand.
Tom wants to save some cash to use at the store.
Tom decides to pay with his credit card and writes in a tip.
Tom skips out on tipping for the meal service to hold onto enough cash for the store.
Tom's server ends up making a fair amount of money during his shift.
Tom's server does not make enough money to earn a living wage on his shift.