Try try try but don't cry

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 now know that
there are two thousand elements which we cannot use
to make a good light bulb."