I was about to start priming the walls on my new room addition when I noticed the lights weren't working. I did a little investigating, then more, then it stretched into hours, then a day. I finally discovered the problem. The exterior siding had been put on after the wiring was done. For some reason the builder was putting siding on with 3 inch nails. I don't know why. One of the nails missed the stud and went through all three runs of romex right where they were stapled to the stud. If I tried I couldn't do this in 100 years.
I only found it because after hours of trying to figure it out I took a long shot and started looking at where the nails on the siding were placed. I guessed, and hit the jackpot on the first one.