Full Idea
Happiness is defined by Zeno and Cleanthes and Chrysippus as 'an equable flow of life'.
Gist of Idea
Happiness for the Stoics was an equable flow of life
Source
report of Stoic school (fragments/reports [c.200 BCE]) by Sextus Empiricus - Against the Ethicists (one book) II.30
Book Reference
Sextus Empiricus: 'Against the Physicists/Against the Ethicists', ed/tr. Bury,R.G. [Harvard Loeb 1997], p.399
A Reaction
These are the great Stoics. Sounds a bit dull. The old Chinese curse: 'may you live in interesting times'. An equable life could be achieve by never attempting anything, and never getting involved in anything. I don't agree with this idea.