Full Idea
Diogenes of Babylon defined the goal to be rationality in the selection and rejection of the things according to nature.
Gist of Idea
The goal is rationality in the selection of things according to nature
Source
report of Diogenes (Bab) (fragments/reports [c.180 BCE]) by D.L. Blank - Diogenes of Babylon
Book Reference
'Encyclopedia of Classical Philosophy', ed/tr. Zeyl,Donald J. [Fitzroy Dearborn 1997], p.193
A Reaction
This captures the central Stoic idea quite nicely. 'Live according to nature', but this always meant 'live according to reason', because that is (as Aristotle had taught) the essence of our nature. This only makes sense if reason and nature coincide.