My expensive cpu lesaon. The person that designed lga 2011 had the brilliant idea to make notches on the cpu almost symmetrical. So it is possible with juuuust a tiny bit of force to put it the opposite way.
While trying to get as many of those machines working as possible, I unseated the CPU (can't remember why), and I guessed the orientation wrong when putting it back into the machine. I don't remember seeing or smelling any literal magic smoke, but it must've gotten let out, because that machine never booted again.
Luckily, that wasn't any kind of new hardware. I've got an active imagination though, and it always comes to mind when I am working with new and expensive equipment.