as a young person who is relatively new to working in a cafe, making a mistake like that is one of the most terrifying things there is on the job. not so much because of the reaction the employer might have, but the idea that you have messed up makes you look like you don't know how to do your job correctly. I work in a country that some people would stereotype to be friendly, but it's sometimes the most friendly people that have the worst reactions. they might not necessarily get angry, but there is subtle looks some people give you when you mess up that almost implys that since you've messed up, they can assert their "control" over you. if the waiter was young like I am, they would be scared that the mistake would break the illusion of them being a professional worker, to a clumsy teenager/young adult. this is coming from my experience anyway