We label parcels 'fragile' but have no word for the opposite — not strong, which survives shocks unchanged, but something that improves because of them. Your muscles are the everyday example.
Every observed swan was white until Australia. No amount of confirming evidence establishes a universal rule — and the most confident moment is often the one just before the record breaks.
Lifting weights tears muscle, and the tearing is the point. A small dose of something harmful can trigger a repair response that leaves you stronger — but only under two specific conditions.
A bridge expecting ten tonnes is built to hold fifty. The extra capacity will likely never be used — and it is not there for unusual lorries. It is there because the calculations might be wrong.