Messing up the fuel selectors in the Baron crash falls well within the parameters of human error - and is far from the only case where engine(s) quit with fuel in the tanks somewhere and the crew did not figure out why before terra firma got in the way.
If all of those poor pilots had previously been herded into the loony bin, the psychs would have been collecting so many false positives that anybody volunteering to fly anything would have been instantly committed.
Airplanes do crash regularly because of various forms of human error -- including how engineers program various black boxes to make airplanes "pilotproof".