I read a parable about a locksmith: Early in his career, he's not good at picking locks. It takes him a long time and is obviously a lot of effort. People who call him out can see how much work he's putting in and give him tips that reflect the effort they see. Later, he gets good at picking locks and it looks effortless, so his tips decline as he improves.
The point the author didn't intend to make is that in the US, tipping makes service seem like entertainment.