So true: "2 captains and a check pilot = potentially disastrous if something goes wrong"
We are all human beings: to operate efficiently our brain needs no distractions, if we know we are under scrutiny and detailed observation, the pressure and anxiety can interfere with our brain functions to the point that we can make silly basic mistakes which would have not been done if we were not under observational pressure.
Examples: some people do all wrong if they know they are being observed from behind whilst they work on a computer, some people end up doing all wrong if their phone call is being monitored and they know about this, and so on. Many real life examples (driving exams, etc).
We are all human beings. Full concentration is achieved when there is minimal external interference.
During a real emergency it would be better not to be
under observation or examination. Anxiety status would certainly not help to get out alive.
