From Rohan Healey's Greeks to Geeks: Practical Stoicism for the 21st Century:
"For How Much is Lettuce Sold: The Little Epictetus Inside Your Head
Epictetus: 'Is anyone preferred before you at an entertainment, or in a compliment, or in being admitted to a consultation? If these things are good, you ought to be glad that he has gotten them; and if they are evil, don't be grieved that you have not gotten them. And remember that you cannot, without using the same means [which others do] to acquire things not in our own control, expect to be thought worthy of an equal share of them. For how can he who does not frequent the door of any [great] man, does not attend him, does not praise him, have an equal share with him who does? You are unjust then, and insatiable, if you are unwilling to pay the price for which these things are sold, and would have them for nothing. For how much is lettuce sold? Fifty cents, for instance. If another, then, paying fifty cents, takes the lettuce, and you, not paying it, go without them, don't imagine that he has gained any advantage over you. For as he has the lettuce, so you have the fifty cents which you did not give. So, in the present case, you have not been invited to such a person's entertainment, because you have not paid him the price for which a supper is sold. It is sold for praise; it is sold for attendance. Give him then the value, if it is for your advantage. But if you would, at the same time, not pay the one and yet receive the other, you are insatiable, and a blockhead. Have you nothing, then, instead of the supper? Yes, indeed you have: the not praising him, whom you don't like to praise; the not bearing with his behaviour at coming in.'
This passage describes yet another way we often torment ourselves needlessly. It's basically the idea of having your cake and eating it too.
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In all your dealings with the world there is an exchange, a compromise . . . But once you have made your choices, look at, and be happy with what you have gained, or retained, and don't lust after having both or you will be miserable.
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Don't forget what you have, and what it would cost to have what another is in possession of, nothing comes for free, there is always a price to pay be it in money, time, or lifestyle choices. So often we get carried away by the appearance of things, especially in regard to jealousy and envy, but always remember that everything comes with a cost."