What if the understanding you have is fundamentally wrong? That's the point - he wasn't saying that he had a replacement for Black-Scholes. He was saying that a

What if the understanding you have is fundamentally wrong? That's the point - he wasn't saying that he had a replacement for Black-Scholes. He was saying that anything based on Gaussians is broken beyond any utility, no matter how tempting it is to believe the theoretical story behind it. You don't need to be a tailor to see that the emperor has no clothes. That's the tragedy, in a way. The portfolio managers were saying that they needed a tool to assess risk, and that any tool was better than nothing. Mandelbrot turned around and proved that a bad tool is worse than nothing, and got ignored because it might take another hundred years of research before his ideas can get turned into a practical tool.