Every day, every component gets a day older. Some of them will break. Some of them, perhaps, will short out when a high-energy nucleus hits them in the wrong way. Some things may be destroyed by micro-meteorites. We'll do our best to avoid it, but perhaps a card or a cable could jiggle loose during launch; or, perhaps, something unexpected could happen. Read the next section (The Space Environment) to see some of the things that may go wrong.
Even if something goes wrong, something unexpected or unlucky, we want AMS to keep taking data. For this reason, all of AMS is designed in a redundant way. If one critical component fails, a backup component takes over and ensures that we stay functional. We launch two of each computer, two of each valve, two of each cable; if one fails, its partner takes over. We divide up the detectors themselves (which of course are too heavy to multiply) such that, if one part breaks, the others continue taking physics data. This redundancy is one of the things that distinguishes AMS from ground-based experiments.