Remember the Russian spacecraft—headed for Mars—that failed mysteriously recently not long after takeoff? There were a few suggested reasons for the failure—such as effects due to cosmic rays from the sun, and the result of exposure to US radars
Well, turns out the reasons were more prosaic than that–the craft failed due to a programming error! Two channels of the onboard computer rebooted simultaneously—which evidently they were not supposed to do.
Amazing how the most complex missions can be undone by relatively simpler errors—remember the NASA Mars mission that failed due to a mistake in the units used?