Learning from Mistakes
Thomas Edison tried two thousand different materials in search of a filament for the light bulb. When none worked satisfactorily, his assistant complained, All our work is in vain. We have learned nothing.
Edison replied very confidently, Oh, we have come a long way and we have learned a lot. We know that there are two thousand elements which we cannot use to make a good light bulb.
Moral: We can also learn from our mistakes.