I very nearly turned a Seneca into a two tonne glider once.
My instructor had turned off an engine using the fuel cut off switch without saying anything. When the engine died I thought: 'ah ha we have an engine failure' I went through the whole drill to 'secure' the engine, since the fuel had actually been shut off I did everything for real, feathered etc, then went to turn off the fuel on the shut down engine (which of course was already shut off but I did not 'know' this as part of the exercise). I'm not sure why but I think something in my brain thought 'oh that switch is already in the off position therefore it must be the other one that needs switching off...'
About 10 seconds later the other engine started to die, quick as a flash my instructor realised what I had done and restored fuel to the other engine.
What is sometimes seen in aviation is that for some reason, once in a blue moon usually, the mind, for no good reason just decides to do something different from what it usually does.
...Shuts down the wrong engine, raises the gear instead of the flaps after landing, grabs the mixture instead of the the throttle when reducing power etc...
To an extent aircraft cockpit design can reduce the likelihood of these sorts of things, for example having the gear and flap handles in different and representative shapes, having different style knobs on the different engine controls and having fuel levers that actually match the 'direction' that the fuel is going to flow.