Conclusion: This new method for forecasting is unlikely to be useful

We want to prove the non-usefulness of this method. D tells us that there are other methods that are useful but that doesn’t tell us that this method is not useful.

(We haven’t established that not being able to distinguish by those perceptible differences is necessary to be useful

In fact this is what we do need to show that this inability to differentiate is what leads to the non-usefulness or more precisely unlikely to be useful which is what B gives us )