I did a kitchen remodel for a friend a couple of years back. They had previously had pulldown attic stairs added, which required cutting joists. On my first trip up there, I put my hands on the joists to pull myself up, switched on the pullchain light, then looked down. There was a piece of 12/2 NM cut squarely, not reinsulated, not two inches from where I had placed my hand. My tick tracer told me it was hot!
I don't know what its purpose had been, but apparently it had been cut by the dimwit who installed those stairs.