Lose investments cheerfully. Seneca, Epistles 5.42.8-10

Seneca advises Lucilius not to mind merely financial losses, the kind of material losses that cause no physical damage to life and limb. If you cannot afford to lose something, then you should not trade it (to anyone, in any market, for any reason).

Idem itaque in omnibus consiliis rebusque faciamus quod solemus facere quotiens ad institorem alicuius mercis accessimus: videamus hoc quod concupiscimus quanti deferatur. Saepe maximum pretium est pro quo nullum datur. Multa possum tibi ostendere quae acquisita acceptaque libertatem nobis extorserint; nostri essemus, si ista nostra non essent. Haec ergo tecum ipse versa, non solum ubi de incremento agetur, sed etiam ubi de iactura. Hoc periturum est. Nempe adventicium fuit; tam facile sine isto vives quam vixisti. Si diu illud habuisti, perdis postquam satiatus es; si non diu, perdis antequam assuescas. Pecuniam minorem habebis. Nempe et molestiam. Gratiam minorem. Nempe et invidiam. Circumspice ista quae nos agunt in insaniam, quae cum plurimis lacrimis amittimus: scies non damnum in iis molestum esse, sed opinionem damni. Nemo illa perisse sentit sed cogitat. Qui se habet nihil perdidit: sed quoto cuique habere se contigit? Vale.

In every scheme and business, let us adopt the same manner that we are accustomed already to use when we approach a merchant: we should see how deficient, how defective & imperfect, are the wares that we desire. Often the greatest purchase is that for which nothing at all is given. Many things I can show you, which once acquired and accepted shall wrench from us our liberty. We would belong to ourselves, if only they did not belong to us. As you deal with these things, consider not merely how to increase your possession, but also how to be rid of it. “But it will go to waste!” Its arrival was purely accidental; you will live as easily without it as with it. If your loss comes after long possession, then you are already satisfied: you have taken all you can. If you have only had possession a little while, then you haven't had time to adjust, and won't miss the loss. “You will have less money!” And less bother. “You'll lose public favor!” And envy, which is better lost. Look around at the stuff that drives us to madness, the goods whose loss elicits the most tears. You will recognize that the real damage is not in the things themselves, but in our attitude and opinion of them. Nobody feels purely financial losses in the flesh: we can only sense them as mental fantasies. The man who keeps himself has lost nothing. But how many are able to keep themselves, really? Farewell.