Your theory is correct in normal circumstances - in a long career,from time to time after doing a pre-departure inspection I have felt uneasy and gone back again and found something not right. I think that the brain carries a picture of what is expected to be seen,notices a difference and gives the feeling of unease,prompting another look. That is about as simple as I can make it. As far as the hydraulic failure incident is concerned that was a one off.I believe it was just a coincidence as there could be no way that I could have sensed an imminent failure. A failing pump does not make a noise or any other indication,I was sound asleep behind a curtain at the rear of the upper deck. The only other time I have been able to forecast a systems failure is when on a couple of occasions I have observed F/Es doing stupid things that were bound to give problems.