I was an AV geek in high school. One day, a teacher explained to us that she was going to play a phonograph record, but at the same time she was going to record it on tape. She told us that we had to be perfectly quiet while it played and I could see why. The way she had set up to tape the record was by placing the microphone for the tape recorder in front of the phonograph's loudspeaker. I showed her how to jack the record player directly into the tape recorder without using the microphone, eliminating the need for anyone to worry about disturbing the recording. She accepted that my way would work, since I was after all the AV geek, but she insisted that everyone remain perfectly quiet, "just in case."
You might suspect that this teacher was simply trying to ensure attentive silence during the playing of the record, but I can assure you that she did not understand what I had done nor that it was impossible for any noise we might have made to get onto the tape.
James Thurber tells a similar story about his grandmother, in the early days of electric lighting, going around the house tightening the light bulbs, "so the electricity won't leak out."
I learned a couple of lessons from that experience. Using my knowledge, I had accomplished the primary goal of ensuring a clean recording for the teacher. That I was unsuccessful at teaching her about the nature of what I had done was not, in the scheme of things, particularly important. I also learned that it is common for people in authority to know less than the people they are supposed to lead. That particular teacher was very stupid and everyone knew it. I learned that people often have authority they don't deserve, but they can still mess you up.
"Just in case" is often used to defend ignorance. I'm frequently struck by people who have only the vaguest idea about how things they use every day -- cars, computers, mobile phones -- actually work. They try to make sense of their world as best they can. We're all like that about something. When you are trying to make sense of the world it's good to remember that there are things you know that other people don't and things they know that you don't. The lesson to take away is humility, not superiority.