Full Idea
One's own interest is a relative good, nobility a good absolutely.
Clarification
'Nobility' is what is 'kalon', or fine or beautiful
Gist of Idea
Self-interest is a relative good, but nobility an absolute good
Source
Aristotle (The Art of Rhetoric [c.350 BCE], 1389b37)
Book Reference
Aristotle: 'The Art of Rhetoric', ed/tr. Lawson-Tancred,H.C. [Penguin 1991], p.175
A Reaction
The key idea in the whole of Greek moral theory is the concept of what we can call a 'beautiful' action. Such things, or course, tend to be visible in great actions, such as sparing an enemy, rather than the minutiae of well-mannered daily life.