The ability to distinguish unlikely from impossible protects you from both panic and arrogance.

Unlikely and impossible feel similar from a distance and behave completely differently. Treat the unlikely as impossible and you will be blindsided by the thing you ruled out. Treat the impossible as merely unlikely and you will spend your life bracing for events that will never arrive. Holding the difference gives you a middle setting: prepared without being frightened, confident without being naive.

When a worry grips you, put a rough number on it. Not precisely, just an order of magnitude: is this a once-in-a-decade thing or a never thing. Then ask what a proportionate preparation would look like and do only that. The point is not to stop worrying but to size the response to the actual risk.