As an interviewee: if you are failing interviews chronically, you should contact some of the interviewers you felt you connected best with (personally/directly) and ask for feedback. No guarantees for any individual, but if you talk to many people, you may get feedback from somebody.
As an interviewer: Be brave. From a CYA perspective, you may wish to avoid electronic communication about anything that could be seen as conspiratorial. (ie. Don't send a text about having somebody deflate a football)
In general: Sometimes you don't get the job for reasons that have nothing to do with your interview performance. Maybe they had a choice of two or three people they liked and there was nothing wrong with you but they liked somebody else better. In some settings (academia and government) somebody has been pitching management for six months, a year, or more, to create a job for themselves, but they have to interview other people anyway because policy/the law says so.