" Practically, it is most helpful when one wants to find out the type to ask, what is the greatest cross for the person? Where is his greatest suffering? Where does he feel that he always knocks his head against the obstacle and suffers hell? That generally points to the inferior function. Many people, moreover, develop two superior functions so well that it is very difficult to say whether the person is a thinking intuitive type or an intuitive type with good thinking, for the two seem equally good. Sometimes sensation and feeling are so well developed in an individual that you would have difficulty in ascertaining which is the first. But does the intuitive thinking person suffer more from knocking his head on sensation facts or from feeling problems? Here you can decide which is the first, and which the well-developed second, function. "

― Marie-Louise von Franz , Lectures on Jung's Typology