The external feedback is just the last step in the chain, though. What the audience does on that night hardly matters: you got them to buy tickets, and the rest

The external feedback is just the last step in the chain, though. What the audience does on that night hardly matters: you got them to buy tickets, and the rest is knowing that you execute well on that performance, which is something the cast and crew have to know for themselves, because so many mistakes go unnoticed and just result in the performance being a little bit less polished. When the seats are empty, that's the real marker of failure. But you can't get that information directly - flops are always a case of "couldn't see it coming". You can aim to derisk by following convention, but that's treading water and makes you an undifferentiated performer. You have to set principled benchmarks for yourself to excel because the feedback is going to be too sparse otherwise. That's the real struggle throughout all the arts. It's not on other people to set them for you.