The practical good and medical practice
In the first book of the Nicomachean Ethics Aristotle considers the nature of "the good", i.e. the highest ethical value. He examines an abstract notion of the good, "the form of the good", which was developed by his teacher, Plato, and rejects it in favour of a practical conception of the good based on what he considers to be the function of human beings. In the following passage he makes an interesting comparison between the practical good and medical practice.
The practical good is more useful than the ideal good
It would perhaps seem that it is better to get to know the ideal good in order to gain and practice other goods. Using it as an example we will more easily find out the things which are good for us, and knowing this will acquire them. This argument has some plausibility, but it is incompatible with the sciences. They all aim at some good, and, looking for what they lack, leaving aside knowledge of the ideal good. If it were so helpful it is unlikely that all the experts would not know it or even seek to find out what it is. It is unclear whether a weaver or a carpenter would be helped in his own craft by knowing the ideal good or whether someone becomes a better doctor or general by contemplating the ideal good. A doctor does not seem to consider health in the abstract, but the health of a human being, or rather the health of a particular human being. It is an individual person whom she treats.
Aristotle, Nicomachean Ethics, I, vi, 14-23, translated by Paul Crichton