The safest-looking surface can conceal the failure that has not reached it yet.

A sound-looking surface tells you about the surface. Corrosion, rot, and fatigue work from the inside out and become visible only in the last stage, which means appearance is a lagging indicator of condition. What looks fine is often just failing invisibly.

This is worth remembering about anything you assess by how it looks, including people and organisations. The calm surface may be genuine and it may be the part that has not given way yet. Ask what would show early, and go and look at that instead. Waiting for visible signs means waiting until most of the damage has already happened.