We've all had those moments, where you just say "Doh!" and want to smack yourself for having missed the obvious. But then there is that feeling of relief when you realize, "oh, THAT'S all that was wrong?!" and you're glad the solution was so simple.
Our engineering group once had a nice color LCD display built into a device. The client had picked it but it looked a bit blurry.
Turned out it had a protective film over it
which the client pointed out to us.
I have seen this effect all too often with engineers trying to debug a problem. The rush to find the solution oftentimes hinders the finding of the problem :}). When I was working on a system level intermittent problem a few years ago with an array processor prototype (OK many years ago!), I struggled to find the root cause of the failures, for what it seems like weeks only to find that my testing/setup missed the problem. The problem turned out to be with the timing of a particular chip (too hot with the board plugged into the system, cool enough on an extender board to work). I would not have found the problem if it were not for my "just walking away" for a couple of days. I went back after a long weekend with a fresh brain, and followed my gut level instincts. Only then was I able to diagnose the real problem.