Biggest '40 hours' joke I know is that after 40 hours and $10k+, a check ride and two written tests, a pilot still doesn't know how to fill a plane with gas
It isn't just limited to single engine piston airplanes.
I started flying the Challenger 605 in September. In initial (simulator) type rating training, "how to fuel" wasn't covered in any practical sense, since of course there was no refueling of the simulator. When I started flying it, at first all of my flights started and ended at home station (*), where our flight line maintenance folks would take care of the fueling. So after several flights in it, I realized I had no idea how to set the fuel panel and other necessary details about how it all works, and asked one of the guys to delay the fueling on my next trip until I was there and could be trained.
* Yes, a flight without a landing at other than home station in a midsize jet seems weird, but we usually don't need to land to accomplish our mission.
It's like when my daughter was about 3, we were in a hotel. She uses the bathroom and comes out looking very troubled.
"What's wrong honey?"
"There's no soap!"
I go into the bathroom, sure enough there's the the bar of soap I had unwrapped earlier, next to the sink.
"It's right there, silly"
"Where?"
"That bar of soap right there."
"Bar soap? I don't know how to use bar soap!"
Which seems really ridiculous and still makes us laugh, but I paused a moment before responding, and realized that, actually, she probably didn't know how. All of the soap at our house is in the pump containers. So she may never HAVE used bar soap, and I never thought of it to teach her. It wasn't on my "child training syllabus". It was then that I realized MOST things are taught, not intuitive or obvious, and to blame the teacher (i.e. me) for lack of knowledge, not the student.