Contemplating love, loss, and mortality
If you are kissing your child or wife, say that it is a human being [a mortal] whom you are kissing, for thus when they die, you will not be disturbed. — Epictetus
This is of the most notorious passages in the ancient Stoic literature. It comes from the famous Encheiridion or Handbook (§ 3). Epictetus intended his advice to be taken literally, as basic psychological training for the students of Stoicism he was addressing.
He means that we should silently remind ourselves of the fact, when kissing our loved ones, that they are mortal. Nothing about them is immune to change, and eventually they’re going to die.
Based on his comments elsewhere, incidentally, it seems unlikely that he meant we should expect not to be disturbed at all by the loss of a loved one. Rather he’s advising his students on how to increase their emotional resilience to loss by reducing their sense of attachment, within certain bounds.
In the same passage, he explains that this strategy should be applied in a very general way to anything we love or find pleasurable. We should pause to consider its true nature, avoid adding strong value judgements or emotive language, and just stick to the facts. We should love in accord with reason, by being brutally honest with ourselves. The facts are that the character of our loved ones may change over time, and one day they will be no more.