Have you ever been holding an umbrella after it stopped raining, without noticing?

To fix this problem, let us design an umbrella with a rain sensor.

Of course, a sensor is expensive and adds complexity. A better design is to put a hole in the umbrella.

This hole-based sensor is not very sensitive, so we should maximize the size of the hole. This removes the canopy entirely.

Next, we optimize cost. Once the canopy is gone, the stick is unnecessary, so we remove that too.

As a bonus, the resulting umbrella holds itself. It requires no hand to keep it upright and is therefore ergonomic. It is also completely resistant to being blown away by the wind.

We have now designed an umbrella with provably optimal rain sensitivity, cost, ergonomics, and wind resistance. By giving up just a little rain protection, we have maximized every other performance metric.

The design has already achieved extraordinary commercial success. Billions of people use it every year.

Its success rests on a deep psychological truth: suffering comes not from the rain, but from our expectation that we must not get wet.