Final answer:
The term describing the strength of character that leads to flourishing and eudaimonia is 'virtue' or 'arête'. Virtue is developed through habituation and encompasses qualities like courage and wisdom, central to Greek and Roman philosophical traditions.
Step-by-step explanation:
Ancient Greek and Roman philosophers like Plato, Aristotle, and the Stoics argued that living virtuously leads to a flourishing life, which is the essence of eudaimonia. In this view, virtue isn't simply about individual good actions but refers to a more comprehensive moral character embodying qualities such as courage, justice, temperance, and wisdom. This character is developed through habituation, where consistent practice of virtuous acts leads to a stronger and more virtuous self. Moreover, individuals cultivate virtue through their actions and choices, although the Stoics believed that even in the face of adversity, virtue remains intact and ensures flourishing. The development of virtues is said to help individuals better deal with life's misfortunes and contribute toward a fulfilling life. Virtuous friendships, as in Aristotle's concept of friendships of character, are highly valued and seen as strengthening one's capacity for virtue and well-being.