The end of the last decade saw a media frenzy over possibility of an H1N1 flu pandemic. The frenzy turned out to be misplaced, but it did serve to remind us of a basic truth: that a healthy body can be stricken with a fatal disease which to outward appearances is nearly identical to a common yearly annoyance. There are lessons here for quantum mechanics. In the history of physics, there has never been a healthier body than quantum theory; no theory has ever been more all-encompassing or more powerful. Its calculations are relevant at every scale of physical experience, from subnuclear particles, to table-top lasers, to the cores of neutron stars and even the first 3 min of the universe. Yet since its founding days, many physicists have feared that quantum theory's common annoyance – the continuing feeling that something at the bottom of it does not make sense – may one day turn out to be the symptom of something fatal.