Because that’s what it basically comes down to, according to the military experts The New York Times's David Brooks interviewed for his op-ed piece on Afghanistan policy.

They were, he found, almost uniformly uninspired by questions about the President’s policy choices. What they worried about - what really kept them up at night - was whether he was made of the right stuff.

Their first concerns are about Obama the man. They know he is intellectually sophisticated. They know he is capable of processing complicated arguments and weighing nuanced evidence.

But they do not know if he possesses the trait that is more important than intellectual sophistication and, in fact, stands in tension with it.

They do not know if he possesses tenacity, the ability to fixate on a simple conviction and grip it, viscerally and unflinchingly, through complexity and confusion.

It's worth reading the whole article, here.