Automation can mitigate the effects of fatigue because it doesn't get distracted, lose situational awareness or suffer from any of the other very elementary human frailties such as vertigo or fear. Automation is a fine and "loyal" servant, used wisely and intelligently.
The problem is that MOST automation has NO situational awareness, as situational awareness is recognizing not only where you ARE, but remembering where you WERE and knowing the difference. The way auto pilots and most flight systems are written now is as if you jump out of a plane on a skydiving trip. While freefalling, your two feet for a moment are firmly on the back of the fellow sky diving below you. as he spreads his arms and decelerates, you gain 'gravity' relevant to his speed and thus, UNBUCKLE AND DISCARD YOUR PARACHUTE *good luck with the remaining 10,000 feet, sucker!
Ludicrous? (not the singer) but that's how A/P ,F/C software is written today! Sure, there are minor bits of pseudo intelligence , what I call 'digital common sense' like storing the last 15 seconds of a probe's readings to be able to discard 'noise' of intermittent fluctuations but that's not applied across the board. Most sampling and decision making is using
that very instant of data and until corrected will allow a plane coming in to land: 800ft, 700ft, 600ft,
-82 ft!!! to instantly cut engines (we already landed, whoopee!) and fall short of the runway. Obviously, if the autopilot had situational awareness, it would discard the sudden drop from 600ft to -82 ft as being unsustainable and invalid and do something else (automatic TOGA?) handing over to the pilot WOULD not be a good option, I think as there would be no time.