Full Idea
Stoics begin ethics with concern for one's own happiness, and end up claiming that in morality one will be indifferent between one's own interests and those of 'the remote Mysian'.
Gist of Idea
Stoic morality says that one's own happiness will lead to impartiality
Source
report of Stoic school (fragments/reports [c.200 BCE]) by Julia Annas - The Morality of Happiness 2.7
Book Reference
Annas,Julia: 'The Morality of Happiness' [OUP 1995], p.128
A Reaction
Makes sense, if pursuing our own happiness is doomed, and the best we can manage is indifference.