Aristotle's Nicomachean Ethics -

For Aristotle, the unique human function is the activity of the soul in accordance with reason .

Virtue is not something we are born with; it is a developed through practice. Aristotle's Nicomachean Ethics

We become just by performing just acts and brave by performing brave acts. For Aristotle, the unique human function is the

True happiness is not a temporary emotion but a state achieved over a complete life. The Nature of Virtue (Arete) Aristotle's Nicomachean Ethics

Just as a knife is "good" if it cuts well, a human is "good" if they perform their unique function well.