Your last sentence is key, and seems to be something that everybody forgets about. You have a great deal of redundancy so that a problem in the air doesn't get you killed. But the whole point of that redundancy is defeated if you're relying on it from the beginning of the flight. Therefore it's common, and reasonable, to have issues that wouldn't cause any trouble in the air, but which prevents you from flying to begin with.

Imagine if the speedometer in your car failed. You shouldn't drive it until you get it fixed, but it won't kill you if it happens while you're on the highway.