Belts & Chains
Serpentine belts, timing belts, tensioners and interference engines.
Two very different components get called "the belt." The serpentine belt runs the accessories — alternator, water pump on many engines, power steering, AC compressor — and if it breaks you lose charging and often cooling, but the engine survives. The timing belt synchronizes the crankshaft and camshafts, and on an interference engine breaking one bends valves.
Timing chains replaced timing belts on most modern engines and are designed to last the life of the engine, but they depend entirely on oil pressure and clean oil. Stretched chains and failed tensioners are a well-documented consequence of extended oil neglect on several direct-injection engine families.