Isn't it fairly well-established that at least some chronic pain is caused by, basically, the pain circuits in the brain going off on their own, long after the original cause was resolved? (Such as phantom limb pain.)

But that pain is still real, and not amenable to "thinking it away." The V. S. Ramachandran book I read discussed a treatment of his for phantom limb pain which essentially changed the brain's perception of itself, and so made it stop sending pain signals. But it didn't work in all cases, and was much more sophisticated than "think it away." (It involved an elaborate arrangement of mirrors.)