Rationality has its limits. We all know that daily exercise is good for us, and that it's something we should be doing. It's pretty clearly the "rational" choice. But can rationality actually get us to exercise every day? Is there some further bias we can eliminate that will enable us to drag our asses to the gym even when we're feeling completely exhausted? I doubt it -- there's just nothing much more that rationality can do for us in that department. A related (and rhetorical) question: are fat people fat because they're rationally deficient in some sense? We need to be careful not to downplay the extremely powerful and seemingly ineradicable influences of emotion and subjective experience (urges, fatigue, impulses, etc.) in our day-to-day decision-making.