Not sure what the point is of supposing the experience of posters. Somebody who knows only the theory has plenty contribute IMHO. To coin another naff saying "The best pilots make the worst mistakes".
With regard to commercial vs private ops, I don't see the distinction other than SOPs are an amalgam of experience of considerable depth. Not some contrived H&S initiative.
The common sense angle is the usual backstop when all other attempts at reasoning have failed
When the term is used it usually implies that you don't know the answer to the problem, but that you can arrive at an unverifiable good decision by interpolating what you do know based on some subjective values (hopefully you get my drift, words aren't my strong point). The Mayday advocates are saying that there are numerous factors that can mess things up and that as an individual in a non-normal situation with a failed critical component that at best adversely affects the controllability and performance of the aircraft, your first port of call is for assistance to give you room to understand the problem and confirm that the failure is as normally non-normal as much as one can hope.