1. Theory of Art: Much of what looks like "selling out" is actually an ageing effect.
2. Theory of Literature: There are, basically, three features of a novel; style, story, character. When an author gets two right and does not mess up the third too badly, the book's fine.
3. Theory of Statistics: The main function of significance tests is to allow researchers to treat coefficients as though they were zero, which simplifies things wonderfully.