Epictetus, Golden Sayings 98

Nevertheless, a man should also be prepared to be sufficient unto himself—to dwell with himself alone, even as God dwells with Himself alone, shares His repose with none, and considers the Nature of His own administration, intent upon such thoughts as are meet unto Himself. 

So should we also be able to converse with ourselves, to need none else beside, to sigh for no distraction, to bend our thoughts upon the Divine Administration, and how we stand related to all else; to observe how human accidents touched us of old, and how they touch us now; what things they are that still have power to hurt us, and how they may be cured or removed; to perfect what needs perfecting as Reason would direct.