Failure.
From birth, it's treated as a terrible, taboo thing. Something to be kept at arms length. No one wants to be labeled as one, and nobody wants to associate themselves with one. Everyone's failed once, and everyone's experienced that awful sinking feeling in the pit of their stomach.
But... what if we turned that around? Instead of avoiding it like a plague, why don't we treat it as motivation? As fuel for the fire we each hold? Accept that you'll fail once in a while, and try again. Accept that you need to learn in order to grow.