It seems that the primary reason the space shuttle Discovery didn't launch last week is that one of its fuel gauges was stuck -- it showed the tank was full, when it was actually empty.
This is the exact same problem I had on a car I owned a quarter-century ago, a Datsun 1200 (in the days when the company hadn't yet changed its name to Nissan). The needle in the gas gauge would get stuck on "F," regardless of how much gas I had. The solution? I had to bang on the dashboard in just the right place, and the needle would drop down to the correct level. If I forgot, or didn't pay attention, I'd run out of gas (naturally, this would only occur at the worst possible time, like when I was running late for work, or on a first date).
You'd think that by 2005, NASA's engineers and scientists would have developed a gauge that doesn't stick -- that the technology that takes seven people up to the international space station would be a little more advanced than what I had in that tin can of a vehicle in 1979.
New rule: before starting the countdown, try the old "bang on it" test, and then re-check all gauges. Doesn't anyone at NASA remember "The China Syndrome," in which a nuclear power plant nearly melted down after a technician mis-read the water level because of a stuck gauge needle?
Ask any guy -- banging on it is the first thing you do whenever any kind of equipment doesn't work the way it's supposed to. It's not rocket science, but it still applies.