Rain reveals which parts of a building were only pretending to keep you dry.

Dry weather is generous to bad work. A roof that has never been properly finished looks identical to one that has, and the difference stays theoretical until the first downpour. Then the pretending stops, all at once, in one afternoon. Most things are like this: the quality of a plan, a friendship or a piece of construction is not visible while conditions are easy, and is entirely visible when they are not.

If something matters, find a low-stakes way to test it under load before you need it. And when a bad day exposes a weakness, treat that as information arriving early rather than as a failure on your part.