On the airplane home from "The AD", I wrote in our paper about a data-driven model for the Kepler focal plane. I wrote about the following issue: This model is a data-driven, flexible model of the pixels telemetered down from the spacecraft. As such, the model doesn't contain anything within it that could be interpreted as the "flat-field" or as the "point-spread function" or a "source", let alone a source "brightness". But it is a good model! The question is: How to extract photometry? We have a plan, but it is debatable. The fundamental issue is that data-driven models are, almost by definition, uninterpretable (or at least not straightforwardly interpretable). Insane.