The best teacher of the people of the past

Bill Gates went to eat at a restaurant and after eating, Bill Gates gave the waiter a 5 bounty. After getting the box, the waiter stared at Bill Gates. Bill Gates asked,

"What happened? Why are you looking at me like this?" The waiter said, "Sir, your son gave me a ড 100 box after breakfast here yesterday and you gave me only 5 for his father and being so rich?"