You learn more from failures than you do from successes.
One would think I should have learned a lot by now. Lol!
A lesson learned during WW2 when they realized that 'adding armor to the sides of airplanes because so many of the ones that returned to base were all shot up' wasn't the right approach. They figured out that if they returned to base at all, the number of holes in the sides wasn't the problem - so they reasoned that armoring the engines would increase survivability.