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.