And not that we don't know how. For any ML model, we have a validation data set and it is imperative that we measure how well a model performs on this data set and not the training data set. We know that without a validation, a machine will overfit its model into the data it has. Programmers... do the same thing. We're very good at passing tests and, unless we have a separate independent validation and verification process, we convince ourselves that green tests = quality. So our tests are always green but our backlogs are always red. And nobody seems to notice the contradiction.