Swiss cheese
Yes, Skyhawk, I think that can sum it up. Several apparently minor issues can very quickly add up to a full scale disaster. A perfectly routine flight, can all of a sudden end up difficult when something 'unexpected' happens. We ''train'' for it all to happen, and go flying when hopefully we have assessed everything, and the flight goes to plan.
The issues start, when of course, things screw up. The decision process begins. I once did a really stupid thing. I was flying from Bournmouth into Halfpenny Green, when about 35 miles to run,following the good old magenta, my GPS quit. Guess what, my map was in the back, and I could not reach it. I had not been to that airfield before. Weather was deteriorating, and the wind had picked up.
I then began calculating my drift, calculating everything to try and guide me to the destination. I remember not having the slightest clue where I actually was, and if my track would get me there. Oh, I was also tight on fuel.
I remembered that flight and vowed never to do that again..