I have spoken to physicians who deal with headhunter firms or placement agencies. I have been interviewed by potential employers, who told me they would call me back. When they did not call back, I called them to find out what was going on. They said that they had selected another candidate. There is always another candidate.
Is it because the other candidate was better than me? I don't know; I just don't know. For 25 years now, there has always been another candidate.