I was debugging a TI DSP based board that I designed. It would come up, execute some of my code, and die. It took 3 weeks and lots of back and forth with TIs

I was debugging a TI DSP based board that I designed. It would come up, execute some of my code, and die. It took 3 weeks and lots of back and forth with TIs tech support before I found out that some of the ground pins were left disconnected. The guy that laid out the PCB didn't connect them though they were connected in the schematic. We went back to the PCB editor, zoomed way in, and lo and behold there was this tiny unconnected segment. I don't remember the details any more (this was like 30+ years ago) but I think TI's support was on the right track and I was convinced this can't be true because I had the connection in the schematic. If you probe this with a DVM or a scope it will look connected (because the pins are connected internally) and so it's really hard to find out. This taught me a valuable lesson that anything can be debugged with enough time and persistence. Some things take longer and that's life.