I've noted before:
Loops are at the heart of nonlinearity and the complexity that makes the world interesting, but loops are also dangerous and eagerly avoided by the analyst. Circular reasoning is rightly condemned within pure logic and feedback loops are the bane of every sound system, but loops of self-consistency seem naturally at the heart of how we make sense of the world, and what true understanding is. I think one of Hofstadter's points [in "I Am a Strange Loop"] is that it is only through level-crossing loops that you can break out of simple tautology into true understanding. Perhaps this is at the heart of the "inductive" reasoning that Popper persistently attacks in his "Logic of Scientific Discovery" [...] Economic loops are central to growth; the familiar chicken-and-egg loop is at the heart of life itself.