Human error is a terrible concept, a crutch for bad engineering. Take the story of the VSS Enterprise (SpaceShip Two) that broke up back in 2014. It broke apart because the co-pilot hit a button four seconds early[1]. But if hitting one button four seconds early is the difference between nominal flight and falling from 15 kilometers up without a pressure suit that's really the fault of the person who designed and built the thing[2].
[1]: Outside analysis, sync up a video from an earlier flight with the failed flight, sync'd up to T-0 ignition. The successful flight the co-pilot Alsbury hit the button at T+13s, the fatal flight at T+9s. The fatal flight was the first test of a new engine, so there is some error in this calculation. Wikipedia claims it was 14 seconds too early, but I'm not sure how much I trust the source it cites.
[2]: The feathering device was a clever idea that the designer, Burt Rutan, had: if you fold the entire spacecraft in half while you are up in space then it will pretty much always be in a safe attitude for reentry and you don't need to have much maneuvering authority in space. But below Mach 1.4 there isn't enough aerodynamic pressure to keep the spacecraft from folding in half when you don't want it to (and then the spacecraft gets torn apart by all of the aerodynamic pressure that is there- not enough to keep it from folding in half, but too much to survive if it does fold in half). So they put in these big honking locks to prevent it from folding when you don't want it to. But now you have a new problem: if those locks prevent it from folding while you are up in space now you burn up in the atmosphere because you don't have enough control to keep the spacecraft oriented in a safe manner. So you have to undo the locks above mach 1.4 but before you have burned enough of your rocket fuel that you are committed to going into space: if you try and undo the locks and they don't go, you immediately stop the rocket engine and glide back down to a safe landing. So you have a very narrow window that the button has to be hit, and if you are out of that window you can either accidentally feather and die or fail to feather and die. At a certain point you just have to give up on your clever ideas and admit that they are not helping you.
[1]: Outside analysis, sync up a video from an earlier flight with the failed flight, sync'd up to T-0 ignition. The successful flight the co-pilot Alsbury hit the button at T+13s, the fatal flight at T+9s. The fatal flight was the first test of a new engine, so there is some error in this calculation. Wikipedia claims it was 14 seconds too early, but I'm not sure how much I trust the source it cites.
[2]: The feathering device was a clever idea that the designer, Burt Rutan, had: if you fold the entire spacecraft in half while you are up in space then it will pretty much always be in a safe attitude for reentry and you don't need to have much maneuvering authority in space. But below Mach 1.4 there isn't enough aerodynamic pressure to keep the spacecraft from folding in half when you don't want it to (and then the spacecraft gets torn apart by all of the aerodynamic pressure that is there- not enough to keep it from folding in half, but too much to survive if it does fold in half). So they put in these big honking locks to prevent it from folding when you don't want it to. But now you have a new problem: if those locks prevent it from folding while you are up in space now you burn up in the atmosphere because you don't have enough control to keep the spacecraft oriented in a safe manner. So you have to undo the locks above mach 1.4 but before you have burned enough of your rocket fuel that you are committed to going into space: if you try and undo the locks and they don't go, you immediately stop the rocket engine and glide back down to a safe landing. So you have a very narrow window that the button has to be hit, and if you are out of that window you can either accidentally feather and die or fail to feather and die. At a certain point you just have to give up on your clever ideas and admit that they are not helping you.