"The customer is always right."
I call bull. As a customer and an employee (of course not at the same time), I understand that this concept is barely true. Yes. Employees make mistakes and so does customers too. A little mistake wouldn't really kill off anyone though so at best it would be easy to fix it and just call it a day.
Mistakes that occur in restaurants happen to be fixable in most cases. Situations such as "oh this doesn't taste right ... this is practically not edible ... this drink is ... " can easily be corrected by replacing what was wrong in the first place or if the situation is dire, then place the meal on the house or something similar. Of course this would be the ideal situation, however, every little mistake is reprimanded and treated with severe consequences such as being told off or in worst cases: termination. There are is more than one view to look at this