From Donald Robertson's The Philosophy of Cognitive-Behavioural Therapy:
"As Epictetus puts it, 'I am not eternal, but a man, a part of the whole, as an hour is of the day. Like an hour I must come and, like an hour, pass away' (Discourses, 2.5.13)
Hence, in one of the most startling and controversial passages in Stoic literature, Epictetus recommends that we practice seeing even the lives of our friends and loved ones as transient. He describes this method as 'the highest and principal form' of Stoic training, and the one which marks initiation into the philosophical life. Things that are normally seen as desirable are to be viewed as transient, like an earthenware cup, a disposable object.
'So in this too, when you kiss your child, or your brother, or your friend, never entirely give way to your imagination, nor allow your elation to progress as far as it will; but curb it in, restrain it, like those who stand behind generals when they ride in truiumph and remind them that they are mortal. In a similar way, you should remind yourself that what you love is not your own. It is granted to you for the present while, and not irrevocably, nor for ever, but like a fig or a bunch of grapes in the appointed season; and if you long for it in winter, you are a fool.
So, if you long for your son or your friend when he is not granted to you, know that you are longing for a fig in winter . . . Henceforth, when you take delight in anything, bring to mind the contrary impression . . .' (Discourses 3.24.84-88)
The sage moderates emotional attachment by, philosophically, reminding himself that he is mortal and must die, that his loved ones are mortal, and that wealth and reputation are fickle and transient things, in the hands of fortune and beyond his ultimate control."