The popular medical formulation of morality that goes back to Ariston of Chios, "virtue is the health of the soul," would have to be changed to become useful, at least to read: "your virtue is the health of your soul." For there is no health as such, and all attempts to define a thing that way have been wretched failures. Even the determination of what is healthy for your body depends on your goal, your horizon, your energies, your impulses, your errors, and above all on the ideals and phantasms of your soul. Thus there are innumerable healths of the body; and the more we allow the unique and incomparable to raise its head again, and the more we abjure the dogma of the "equality of men," the more must the concept of a normal health, along with a normal diet and the normal course of an illness, be abandoned by medical men. Only then would the time have come to reflect on the health and illness of the soul, and to find the peculiar virtue of each man in the health of his soul.
Friedrich Nietzsche, The Gay Science, § 120 “Health of the Soul”