By the standards of a strict falsificationism, for example, virtually all the models discussed in this book should have been discarded immediately on the grounds that some of their predictions were empirically false. Yet financial economists did not discard them, and they were right not to. For instance, the Capital Asset Pricing Model (discussed in chapter 2) led to the conclusion that all investors' portfolios of risky assets are identical in their relative composition. That was plainly not so, and it was known not to be so, but the model was still highly prized.

Donald MacKenzie, An Engine, Not a Camera, loc. 60