The Melancholic humor, or black bile, is the humor most prone to aggravation and pathology. In fact, the very word "melancholy" is almost synonymous with morbidity.
Even normal black bile, due to its inherent nature and temperament, is the humor least conducive to the optimal health and nutrition of the organism, even though it does have necessary physiological and metabolic functions to perform. And morbid forms of black bile are even more deleterious in their effects than the morbid forms of other humors. Since black bile is the most effete of all the humors, its pathologies almost always involve excess, with deficiency only a minor consideration.