Everybody gets stuck in loops like this from time to time, but there were several
hints along the way. As many people said, (a) switches just don't fail like that,
(b) if multiple replacements all "fail" the same way, then it's 99.9% likely to be
something else causing the problem, and (c) "operator error" is usually the fault,
especially when it comes to slapping things together using a breadboard. So, 3
lessons in one.