The amount of things to go wrong in an engine is ridiculous. Utterly ridiculous. The smallest of things can utterly doom an engine and the ability of them to keep going for hundreds of thousands of miles simply astounds me. For example:

O2 sensor shows too rich or MAF doesn’t show enough air. Result: car runs lean and melts a piston

Timing belt. A little strip of rubber. Some of the teeth go bye bye. Result: valves high-five the piston

One of the many tiny oil passages gets clogged. Result: crank or rod bearing dries up and spins.

Just those three failures amaze me that they don’t happen more often. The amount of abuse an engine can take before failure completely astonishes me when you weigh it against how seemingly fragile all of it is.