Another facet of ambivalence is, however, present here too. The failure to profit from National General warrants might have been a private disappointment, but there was a sense in which it was a vindication of market efficiency: an apparent profit opportunity turned out not to be real, because market prices were incorporating a piece of information that was not known to Black and his colleagues. `Although our trading didn't turn out very well, this event helped validate the [Black-Scholes] formula," wrote Black: "The market price was out of line for a very good reason" (Black 1989, p. 7). Paradoxically, theorists' practical failure could thus be cited as evidence of theory's robustness.

Donald MacKenzie, An Engine, Not a Camera, loc. 1119