It doesn't take much science-fiction imagination to conceive of creatures -- Klingons, or whatever! -- who work differently. When their equanimity is disturbed, e.g. by relationships falling apart, then they naturally recover their emotional balance after a while, so long as they don't keep dwelling on things. Rather as we heal broken skin so long as we don't keep picking at the scabs, so for our Klingons talking about their problems is like picking at scabs. For them, it is better to "let nature take its course" and for their emotional system to recalibrate itself to the new situation without paying too much conscious attention to the processes. They don't suffer from effects of "repressing" bad experiences, etc.: in fact they function better if they do "repress". Now, if we are very different from our imagined Klingons (as modern therapeutic "it's good to talk" theories suppose we are), then that's an empirical fact about us. And if it is a contingent empirical matter, as it...

Jennifer Church points out a couple of types of a case where irrationally formed beliefs (or degrees of belief, in the over-confidence case) can promote our welfare. Sure there are such cases. But that doesn't affect the original point at stake. There being a few cases doesn't undermine the point that in general false beliefs (because of their content!) are unlikely to lead to successful action,* and so irrationally formed beliefs -- being likely to be false -- are not in general likely to lead to actions which get us what we want. And that is enough to explain why we should in general care a lot about forming our beliefs in a rational way. Which in turnis enough to counter the original questioner's worry that philosophy"uses as its main tool a mechanism [rational thought] that is theopposite of what is most important to us": in general ,rational belief-formation matters for getting whatever is important tous. *Indeed, some attractive views about ascribing content to belief...

Just a footnote to Mark Collier's helpful post. I actually said that irrationally formed beliefs are not likely to lead to actions which get us what we want (rather than cannot get us what we want). And that claim is enough to explain why we should in general care a lot about forming our beliefs in a rational way . Which in turn is enough to counter the original questioner's worry that philosophy "uses as its main tool a mechanism [rational thought] that is the opposite of what is most important to us": in general , rational belief-formation matters for getting whatever is important to us. Even if pockets of irrationality, episodes of self-deception, etc. can -- by good fortune -- happen to promote our welfare.