Aristotle's 'Nicomachean Ethics' accounts for the development of character by emphasizing the formation of habits resulting from action. This process frames the way human beings perceive the world in subsequently acting. Using Aristotle's claim that human life seeks the good, and that the chief good is happiness ('eudaimonia'), I examine how the vices that develop over a lifetime inhibit the possibility of achieving ' eudaimonia.' I then examine the possibility of character transformation towards 'eudaimonia' through true friendship. I argue that friendship has the potential to cultivate virtue, both through the demands its formal structure imposes on us and through the possibility of each friend acting as educator to the other. I qualify the capacity of friendship to transform character by presenting the necessity of risk inherent in intersubjectivity; while friendship is a source of the possibility of change, we are never fully in control of the changes to which friendship subjects us. The life of ' eudaimonia' is therefore never, strictly speaking, something that we can fully secure.