There's a joke about asking skydivers why they'd jump out of a perfectly good airplane and the punch line is that there is no such thing as a perfectly good air

There's a joke about asking skydivers why they'd jump out of a perfectly good airplane and the punch line is that there is no such thing as a perfectly good airplane. Every single plane has things that are broken, things that are inoperative, things that behave slightly out of tolerance. This is true for commercial aircraft the whole way down to single engine trainers. 172s are notorious for having fuel gauges that are basically only good for telling you how many fuel tanks you have and not anything related to quantity of fuel on the plane.