One of the more peculiar practices in American and other Western cultures is the
custom ironclad rule of tipping in certain individual consumer level transactions. Despite being “voluntary,” the consequences of not tipping at all or even just tipping below what is considered acceptable would probably lead you to receiving poor service in the future or an irate waiter running after you as you leave.
Tipping in this sense is definitely not standard in China, but to put it into the Chinese context, it’s best to think of it as the red envelopes stuffed with money (hong bao) that you are expected to pay government officials or your doctor/surgeon to simply do their jobs. JiaYou would probably take issue with this, but I think it’s actually quite similar.