Because if your mind tries to convince you you're incapable of something, and you believe it, then like those two toddlers, you'll begin to feel helpless and you'll stop trying too soon, or you won't even try at all.
Porque si su mente trata de convencerlos de que son incapaces de algo y Uds. se lo creen, entonces como esos dos pequeñitos, comenzarán a sentirse indefensos y dejarán de intentar demasiado pronto, o ni siquiera tratará en absoluto.