 It is noteworthy that the simulation failures mentioned have been detected and corrected within the literature of simulation itself. These are effective critiques within disciplines employing simulation, rather than from outside. An illustration of a such a case with both verification and validation in play is that of the Bruch and Mare critique of the Schelling segregation model and the response to it in van Rooij, Siegel, and Macy (Schelling 1971, 1978; Bruch &amp; Mare 2006; van de Rijt, Siegel, &amp; Macy 2009). Many aspects of that model are clearly artificial: a limitation to two groups, spatialization on a cellular automata grid, and “unhappiness” or moving in terms of a sharp threshold cut-off of tolerance for neighbors of the other group. Bruch and Mare offered clear empirical evidence that residential preferences do not fit a sharp threshold. More importantly, they built a variation of the Schelling model in order to show that the Schelling effect disappeared with more realistic preference profiles. What Bruch and Mare challenged, in other words, was validation: not merely that aspects of the target phenomenon of residential segregation were left out (as they would be in any model), but that relevant aspects were left out: differences that made an important difference. Van de Rijt, Siegel, and Macy failed to understand why the smooth preference curves in Bruch and Mare’s data wouldn’t support rather than defeat a Schelling effect. On investigation they found that they would: Bruch and Mare’s validation claim against Schelling was itself founded in a programming error. De Rijt, Siegel and Macy’s verdict was that Bruch and Mare’s attack itself failed model verification.