"To ask which beliefs make you happy is to turn inward, not outward—it tells you something about yourself, but it is not evidence entangled with the environment. I have nothing against happiness, but it should follow from your picture of the world, rather than tampering with the mental paintbrushes."
I don't understand the justification for this. Is it a utilitarian heuristic? Or what is the reason why happiness must follow from correct beliefs about objective reality.