One of my uni courses our assignments required us to build circuits on breadboards in class - no opportunity to work on it otherwise. My lab partner and I were having problems with one assignment which, despite being wired properly, refused to produce the required output. After checking and rechecking wires, swapping out gates, etc., we were finally down to the last five minutes of class with no idea what to do next. Out of frustration, my partner reach out and scrunched the entire mess of wires in his fists and held them there.

"Try it now"

It worked. He just sat there while I dragged the prof over to evaluate it. As soon as he was done, my partner let go and it stopped working again.