Too many commentators explain the first page of Aristotle's Nicomachean Ethics with an illustration involving a chain of desires, like this one from Christopher Shields, who asks us to imagine that a philosophical friend has asked us why we are buying milk:
If we answer seriously and honestly that we want to buy milk for our morning porridge, and he presses on, wanting to know why we intend to eat porridge in the morning, then we may well answer that we find porridge healthy and delicious, especially with milk, which we may then excuse ourselves to buy. Insensible of our lack of interest, the philosopher may persist, wanting to know why we desire to eat delicious and healthy food. Again, we may respond, that it is because we enjoy delicious food, that eating brings us pleasure, and that we desire health for the obvious reason that health is good—and, lest it be asked, we all desire good things for ourselves. If we have not by now slipped away, we may hear the philosopher posing the same question, earnestly let us allow, ad nauseam, or at least until such time as we say, with exasperation, that we do all these things we do for the sake of happiness.
This sort of account seems cogent. I don't think I could give a more complete justification of milk-buying (except that I don't eat "porridge"). The problem is that it doesn't look anything like Aristotle's illustration of a hierarchy of purposes. The connection between bridle-making and horsemanship has nothing to do with what the bridle-maker wants. It can only be explained in terms of purpose. The purpose of bridle-making is to enable excellence in horsemanship—regardless of whether some individual bridle-maker wants to do so.
This idea of purpose only makes sense in terms of an order that goes beyond the individual. Bridle-making advances the good of a political community, regardless of how it affects the bridle-maker.
But for all that, it is still not clear how a human being can in making a bridle be doing something for a purpose. Sure enough, he is performing an action; sure enough, the action has a purpose, because the bridle is of use, but since this use belongs to the larger community, how can the purpose belong to the individual's action?