On pprune there is a professional pilot that says they had multiple instances of inadverent switching off fuel switches. They do it every startup, shutdown and training captains (the captain on this flight was pilot not flying, he had >10k hours) do it all the time in the sim to trigger engine out scenario during training

Nope, I strongly disagree with that comparison. One doesn't need to pull up a big stick in hand using elbow and shoulder to flip this fuel switch _down_. Would a car's hand brake stop your engine if it's thumb-push-button lock failed silently and you happen to let something fall on it, like a hand? no. But this little fuel switch would.

Bad analogy because pilots are trained and rehearse and practice memory items until they are instinctual.

> impossible by design.

Deflecting that the human is the weakest part of the system. One or other may have panicked and made a mistake, made a mistake unintentionally, went crazy and doomed the flight, or intentionally doomed the flight for some socioeconomic reasons. These are speculative possibilities that we don't know yet, and may never know; we only know what has definitely happened from the evidence per the investigation. It's standing way out over one's feet to declare from an armchair that it was "definitely" X or Y before the investigation is complete.