Letters 9.15

Therefore, although he is self-sufficient, yet he has need of friends. He craves as many friends as possible, not, however, that he may live happily; for he will live happily even without friends. The Supreme Good calls for no practical aids from outside; it is developed at home, and arises entirely within itself. If the good seeks any portion of itself from without, it begins to be subject to the play of Fortune.

Seneca, Letters to Lucilius 9.15, translated by Richard Mott Gummere