1 - Stephen's greatest strength is probably his intellect. He's very, very smart, and generally keeps his mind open enough to accept things and concepts most people wouldn't. His greatest weakness is probably that he's aware of how smart he is. It makes him arrogant and withdrawn from people he views as less intelligent. Unless he makes a conscious effort otherwise, and that comes with all kinds of martyr complexes, too.

2 - He'd probably agree that his greatest strength is his intellect. He would argue that his greatest weakness isn't so much arrogance as it is a lack of self control. He'd e wrong.