[S]ometimes even a return of a previous favor is not fair [but an excessive demand], whenever [the original giver] knows he is benefiting an excellent person, but [the recipient] would be returning the benefit to someone he thinks is vicious.
[T]he excellent person is of one mind with himself, and desires the same things in his whole soul. Hence he wishes goods and apparent goods to himself, and achieves them in his actions, since it is proper to the good person to reach the good by his efforts.
Concord also appears to be a feature of friendship. That is why it is not merely sharing a belief, since this might happen among people who do not know each other. Nor are people said to be in concord when they agree on just anything, on astronomical questions, for instance, since concord on these questions is not a feature of friendship. Rather, a city is said to be in concord when [its citizens] agree on what is advantageous, make the same decision, and act on their common resolution.