“One of the best ways to probe whether you can trust the advice that a theory is offering you is to look for anomalies—something that the theory cannot explain. Remember our story about birds, feathers, and flight? The early aviators might have seen some warning signs in their rudimentary analysis of flight had they examined what their beliefs or theories could not explain. Ostriches have wings and feathers but can’t fly. Bats have wings but no feathers, and they are great fliers. And flying squirrels have neither wings nor feathers … and they get by.”