Since the start of the 1980s, there has thus been a mechanism whereby the identification of anomalies prompts practical action, often by efficient-market theorists or those close to them, which exploits and therefore tends to eliminate those anomalies. Indeed, if that cannot be done if there seems to be no way of exploiting an apparent anomaly there is a sense in which it is not an anomaly, for what the efficient-market hypothesis rules out is not non-random "structure" of any kind, but structure from which excess risk-adjusted profits can be made.

Donald MacKenzie, An Engine, Not a Camera, loc. 451