When research productivity, peer recognition, and publication are prized, another essential quality of a "good" model is that it can be the foundation for further research that is itself tractable without being trivial. All the "orthodox" models centrally considered here had that feature. Consider, in contrast, Mandelbrot's infinite-variance Levy distributions, another case of a cascade that began (with Fama building on Mandelbrot's work, and Fama's students, especially Richard Roll, then taking up the Levy model in their turn) but then lost almost all momentum. Infinite variances undercut standard components of the economist's and econometrician's intellectual toolkit, while what Levy distributions had to offer in their stead could seem dauntingly intractable.

Donald MacKenzie, An Engine, Not a Camera, loc. 1103