Got a request to answer an interesting question on Quora:
The social cost of an interviewer saying, “This is really going badly” is high and the payoff is zero.
The cost of keeping it all smiles and pleasant is low, and the payoff is you feel like a better person.
Most interviews don’t go “bad” or “good” in any objective sense, just as most candidates aren’t “bad” or “good” candidates for jobs generally.
You’re interviewed for your ability to solve a specific problem at a specific company. If you’re not a great fit for solving that problem, you won’t get the job, no matter how good you are generally, or even how great your interview was.
Conversely, if it’s clear you can solve the problem, even a bad interview might not matter much.