Why Occam's Razor

Ensemble theories have received a lot of interest recently as a means of explaining a lot of the detailed complexity observed in reality by a vastly simpler description ``every possibility exists'' and a selection principle ({\em Anthropic Principle}) ``we only observe that which is consistent with our existence''. In this paper I show why, in an ensemble theory of the universe, we should be inhabiting one of the elements of that ensemble with least information content that satisfies the anthropic principle. This explains the effectiveness of aesthetic principles such as Occam's razor in predicting usefulness of scientific theories. I also show, with a couple of reasonable assumptions about the phenomenon of consciousness, the linear structure of quantum mechanics can be derived.