Crew fatigue
I had a check ride that really needed to be done (GA). I paid for the examiner to attend twice. The first time,I had missed a connecting flight and was shattered when I arrived at the field. I called it off despite the expense. On the second occasion I called it of because I had collected food poisoning in the Philippines. On both occasions, despite the cost ( and in Asia the loss of face), I was in no position to perform as I should have and had no option but to cancel. I have massive sympathy for skilled aviators (especially so called Captains) who feel the urge to bow to corporate pressure and fly ac when unfit to do so.
My heart goes out to the crew involved. No one makes deliberate mistakes in the cockpit. We all fly to the best of our abilities.