Once upon a time, Seth Roberts took a European vacation and found that he started losing weight while drinking unfamiliar-tasting caloric fruit juices.

Now suppose Roberts had not known, and never did know, anything about metabolic set points or flavor-calorie associations—all this high-falutin' scientific experimental research that had been done on rats and occasionally humans.

He would have posted to his blog, "Gosh, everyone! You should try these amazing fruit juices that are making me lose weight!" And that would have been the end of it. Some people would have tried it, it would have worked temporarily for some of them (until the flavor-calorie association kicked in) and there never would have been a Shangri-La Diet per se.

The existing Shangri-La Diet is visibly incomplete—for some people, like me, it doesn't seem to work, and there is no apparent reason for this or any logic permitting it. But the reason why as many people have benefited as they have—the reason why there was more than just one more blog post describing a trick that seemed to work for one person and didn't work for anyone else—is that Roberts knew the experimental science that let him interpret what he was seeing, in terms of deep factors that actually did exist.

One of the pieces of advice on OB/LW that was frequently cited as the most important thing learned, was the idea of "the bottom line"—that once a conclusion is written in your mind, it is already true or already false, already wise or already stupid, and no amount of later argument can change that except by changing the conclusion. And this ties directly into another oft-cited most important thing, which is the idea of "engines of cognition", minds as mapping engines that require evidence as fuel.

If I had merely written one more blog post that said, "You know, you really should be more open to changing your mind—it's pretty important—and oh yes, you should pay attention to the evidence too." And this would not have been as useful. Not just because it was less persuasive, but because the actual operations would have been much less clear without the explicit theory backing it up. What constitutes evidence, for example? Is it anything that seems like a forceful argument? Having an explicit probability theory and an explicit causal acc...