The ingredient based explanation for supercell thunderstorms cites moisture, wind shear, instability and lift as the reasons for their formation. I prefer to focus on the big picture. Supercell thunderstorms are a manifestation of nature's attempt to correct an extreme imbalance. The ever ongoing effort to reach equilibrium, or viscosity, is what drives all of our weather, and the force with which the atmosphere tries to correct this imbalance is proportional to the gradient. In other words, the more extreme the imbalance, the more extreme the storm.