If you are puzzled by the requirement to guard the thrust levers and control wheel during flight below 2500', or whatever, do a search for the A300 departure accident at Bucharest, some years ago. Better still, view the AA training video which covers this particular accident and then see if it makes sense.
By all means have faith in the quality of the systems in use but bear in mind that perfection is a VERY elusive quality.
It is still a truism - "NEVER ASSUME, CHECK"