it's been brainwashed into American culture that tipping is required since it has become a cultural norm. in other countries around the world there is no such thing as a "tip" for a waiter.... that's their fukking job.
this is why it's comical for people to pull out their bullshit theories of 5%, 10%, 15%, etc, etc..... none of that shit even exists. you just pulled it out of your ass.
and in other countries they need the tips more than fukking fat Americans do.