> A very easy, relatively pleasant way to get through life in the US if you're well-off enough that you routinely buy coffee in expensive coffee shops: just always tip. Anywhere there's a tip line. You never have to figure anything out, and sometimes people really appreciate it.

Well, unless you are the next person in line who hadn't planned on leaving a tip and now feels guilty/obligated because the person in front of them put down a large tip right in front of the cashier.