A recent empirical study has shown that even experts on the ethics or the law of war cannot reach reasonable convergence on dilemmas regarding the number of civilian casualties who may be killed as a side effect of attacks on legitimate military targets. The purpose of the present article is to explore the philosophical implications of this study. I argue that the wide disagreement between experts on what in bello proportionality means in practice casts serious doubt on their ability to provide real guidance. I then suggest viewing in bello proportionality through the prism of virtue ethics.