In the paper I argue, contrary to the statement uttered once by Martin Seligman, that Aristotelian theory of eudaimonia (one of the key concept of positive psychology) is not subjective and based on uncertain principles. I reconstruct Aristotelian theory of eudaimonia and argue that the concept of good is neither subjective nor objective but relational. It means that a thing, act or action is good if it contributes to one’s eudaimonia. I also pinpoint that the concept of fl ow, which seems to be a “discovery” of positive psychology, must be based on the theory of virtues and the doctrine of human nature, which are the foundations of the Aristotelian view.