Hippocrates De prisca medicina 12

[12] Wherefore, I say, that such constitutions as suffer quickly and strongly from errors in diet, are weaker than others that do not; and that a weak person is in a state very nearly approaching to one in disease; but a person in disease is the weaker, and it is, therefore, more likely that he should suffer if he encounters anything that is unseasonable. It is difficult, seeing that there is no such accuracy in the Art, to hit always upon what is most expedient, and yet many cases occur in medicine which would require this accuracy, as we shall explain. But on that account, I say, we ought not to reject the ancient Art, as if it were not, and had not been properly founded, because it did not attain accuracy in all things, but rather, since it is capable of reaching to the greatest exactitude by reasoning, to receive it and admire its discoveries, made from a state of great ignorance, and as having been well and properly made, and not from chance.

[12] Such constitutions, I contend, that rapidly and severely feel the effects of errors, are weaker than the others. A weak man is but one step removed from a sickly man, but a sickly man is weaker still, and is more apt to suffer distress whenever he misses the due season. And, while the art can admit of such nice exactness, it is difficult always to attain perfect accuracy. But many departments of medicine have reached such a pitch of exactness, and I will speak about them later. I declare, however, that we ought not to reject the ancient art as non-existent, or on the ground that its method of inquiry is faulty, just because it has not attained exactness in every detail, but much rather, because it has been able by reasoning to rise from deep ignorance to approximately perfect accuracy, I think we ought to admire the discoveries as the work, not of chance, but of inquiry rightly and correctly conducted.