Vanity Fair: ... “Nothing comes to my desk that is perfectly solvable,” Obama said at one point. “Otherwise, someone else would have solved it. So you wind up dealing with probabilities. Any given decision you make you’ll wind up with a 30 to 40 percent chance that it isn’t going to work. You have to own that and feel comfortable with the way you made the decision. You can’t be paralyzed by the fact that it might not work out.” On top of all of this, after you have made your decision, you need to feign total certainty about it. People being led do not want to think probabilistically. [emphasis mine]See also Bounded cognition.
Here's a great interview with Michael Lewis, who shadowed Obama off and on over an 8 month period.