All men, or most men, wish what is noble but choose what is profitable; and while it is noble to render a service not with an eye to receiving one in return, it is profitable to receive one. One ought therefore, if one can, to return the equivalent of services received, and to do so willingly; for one ought not to make a man one's friend if one is unwilling to return his favors.
AristotleWhatever we learn to do, we learn by actually doing it; men come to be builders, for instance, by building, and harp players by playing the harp. In the same way, by doing just acts we come to be just; by doing self-controlled acts, we come to be self-controlled ; and by doing brave acts, we become brave.
AristotleHence intellect[ual perception] is both a beginning and an end, for the demonstrations arise from these, and concern them. As a result, one ought to pay attention to the undemonstrated assertions and opinions of experienced and older people, or of the prudent, no less than to demonstrations, for, because the have an experienced eye, they see correctly.
Aristotle