Comment by lcnPylGDnU4H9OF

The problem is that the customer does not know the cost of the meal; they typically rely on the business owner to be upfront about that. Tipping is guilt-motivated drip pricing. The only thing the commenter got wrong is that the restaurateur has to prime the customer with some cost so they can voluntarily add a percentage.

https://en.wikipedia.org/wiki/Drip_pricing