At one of my first jobs we had a big printer that kept jamming in mid-job. Every time our in-house techs showed up it would start working again. Eventually one of the guys taped a wallet-size photo of his face inside the cover of the printer so it was looking at the print head. That machine never jammed again!

http://catb.org/jargon/html/magic-story.html

For anyone who hasn’t heard of the “Magic Switch.”