I used to determine the useful life of jet engine parts for a living to include damage tolerance and repairable limits. It takes an absolutely miniscule amount of damage to compromise a rotating part or airfoil. There are a ton of things like conservative assumptions and safety factors that reduce the risk of catastrophic failures, but those often come down to materials science that we don't fully understand yet. The company I previously worked for just recently discovered (forgive the vagueness, this shit is covered by an NDA) a "thing" which was not previously considered when lifing a certain category of materials. This "thing" has been linked to some pretty crazy disasters, and they're still dicking around about how to approach the problem (the solution is obvious but expensive).