Learn 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.”