Not to appear angry (which is not the same as negativity), but your thesis seems provably false. I admire McGonigal's work a lot, and her positivity is a key part of her personal charm, but she's achieved her success through hard work and brilliant thinking, not Polyanna sunshine. Meanwhile, Zynga's Marc Pincus -- a man filled with rank hatred, festering rage, and a devouring need for revenge -- has become gaming's biggest recent success story. People are motivated by all kinds of emotions, and a whole range of powerful emotions can prompt good work and/or success.