Just an observation: deontic talk, in much of ordinary discourse, is exaggerated. This point is important for epistemology as well as for theories of the rationality of action.
Paradigm example: my wife gets a “free gift” card from retailer X. She already had 2 of them, and went to X to collect on Saturday. Monday another shows up in the mail, and she says, “dang I should have waited–I could have redeemed all 3 together!”
It is obvious that what she says is false–it isn’t the case that she should have waited. The same should be noted, I think, when people say that you should believe the truth. No, that’s false, and the explanation of the mistake is that it is very common to confuse the theory of obligation with the theory of value: it is, in some sense, the best one can do to believe the truth; but in that sense, one has no obligation to conform to whatever is best for one to do. (This post is prelude to another on the connections between obligation and value, one with more theoretical bite–the point of the present post is to keep two theoretical points distinct, the point about the attraction of exaggeration concerning obligation talk and the point about the implications of the best explanation of why it counts as exaggeration.)