Aristotle is obviously one of the great thinkers in history, and he is known for his work in nearly every area of man's life. In addition to his oft-quoted treatises on logic, his legacy includes writings on ethics, mathematics, natural science, oratory, philosophy, poetry, political science, psychology, theology, and zoology. He made distinctions between branches of each kind of science and divided them into these three categories: theoretical, practical, and productive. Each of these sciences have different philosophical concepts which govern them.
Ethics is among the sciences Aristotle believed were practical, and that makes sense. His masterwork on ethics is called Nicomachean Ethics, often called simply Ethics. In this writing, Aristotle emphasizes the need for humans to develop moral character and virtues so they will do good and find happiness.
He makes the case that practicing a discipline (such as philosophy or ethics)must necessarily lead to a goal, and the ultimate goal, according to him is the state he calls eudaimonia, a condition which is best translated as "happiness," though it implies a much deeper meaning than that word has for us today. Happiness to him means a sense of complete human wellness and contentment which leads to a general well being. Happiness to him is the complete excellence which can be achieved by giving attention to the disciplines of science.
Because of that personal and individual goal, it does seem as if the study and discipline of philosophy would be best accomplished simply by personal and individual study. However, while it is certain that man must pursue his own ethical and moral journey, he argues that practicing these things alone (in a vacuum) is a foolish endeavor.
One of the arguments Aristotle makes in Ethics pertains directly to this issue:
Virtue requires habituation, and therefore requires practice, not just theory.... The many, however, do not do these actions but take refuge in arguments, thinking that they are doing philosophy, and this is the way to become excellent people. In this they are like a sick person who listens attentively to the doctor, but acts on none of his instructions. Such a course of action will not improve the state of his body; any more than will the many's way of doing philosophy improve the state of their souls.
His argument, then, is that following a philosophy or discipline takes practice and cannot be accomplished simply by thinking good thoughts. While one may study and think alone, eventually he must practice what he has been thinking about during his solitary study otherwise it is just theory. Putting one's personal philosophy into practice may also be considered a solitary endeavor in one sense; however, it does require the presence of others to polish and refine one's beliefs and philosophy. Even more, without any kind of testing, a philosophy cannot be deemed profitable, successful, or valuable. At some point, personal study and reflection has to erupt into the real world and be tested against other philosophies and beliefs.