Rule #2: We should look for disconfirming as well as confirming
instances of a generalization.
We should actively look for counterexamples: Ss that are not P.
If we have looked hard for negative instances and haven't found
any, we can be more confident of a generalization than we can if
we haven't looked at all.
To continue with the previous example, we should look for Toyota
owners who are satisfied with their cars.