The Black-Scholes-Merton model's one free parameter (volatility) was easily grasped, discussed, and reasoned about. Other models including some of the variants of and modifications of Black-Scholes-Merton that were offered by other financial economists typically involved a mental grasp of, and estimation of, more than one free parameter often three or more. As The Stock Options Manual put it, "the user of these complex models is called upon to deal with more unknowns than the average human mind can handle" (Gastineau 1979, p.

Donald MacKenzie, An Engine, Not a Camera, loc. 726