The trouble one encounters in trying to give a purely behavioral account of virtue explains why the Greek moralists turn to character to explain what virtue is. It may be true that most of us can recognize that it would be foolish to risk our lives and the lives of others to secure a trivial benefit, and that most of us can see that it is unjust to harm others to secure power and wealth for our own comfort. We don’t have to be virtuous to recognize these things. But the Greek moralists think it takes someone of good moral character to determine with regularity and reliability what actions are appropriate and reasonable in fearful situations and that it takes someone of good moral character to determine with regularity and reliability how and when to secure goods and resources for himself and others. This is why Aristotle states in Nicomachean Ethics II.9 that it is not easy to define in rules which actions deserve moral praise and blame, and that these matters require the judgment of the virtuous person.
A soldiers thinking about war may change during his service. For example, after experiencing his first real battle and seeing human beings lying dead or in pain, a soldier might be prompted to embrace pacifism and request or transfer to a non-combat unit. Such a request would not be looked on favorably by his superiors and usually would be denied. Because the man had accepted training as a combat soldier, they would reason, he would be obligated to finish his term of service. Is this reasoning morally sound? Would it be morally acceptable for the soldier to continue fighting, even though he objected to it on principle?”