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In other words, they trust neither their own ability to take the order correctly, nor the kitchen staff's ablility to fulfill.

Yes. And unit tests are only for programmers too sloppy to get everything right the very first time, all the time.

I expect code to be wrong.

I expect writing to have minor flaws.

I expect a sandwich to be a sandwich.

Mistakes that aren't noticed by the time all the food is handed out should be rare, and there's no problem in flagging someone down in that case.

More like they are accounting for any source of human error which is impossible to completely eliminate even with a top-quality staff.