If you forfeit an external possession, make sure to notice what you get in return. If it is something more valuable, never say, 'I have suffered a loss.'  It is no loss if you get a horse in return for an ass, cattle for sheep, a kind act for a little money, real peace in place of idle chatter, decency in exchange for vulgarity.
 Bear this in mind and you will everywhere preserve your proper character; forget it and I assure you that your time here will be a waste, and whatever care you are now expending on yourself will go down the drain.  Very little is needed for everything to be upset and ruined, only a slight lapse in reason.  It's much easier for a mariner to wreck his ship that it is for him to keep it sailing safely; all he has to do is head a little more upwind and disaster is instantaneous. In fact, he does not have to do anything: a momentary loss of attention will produce the same results.
 It's much the same in our case. If you doze off, all your progress up to that point will be negated.  So keep a sharp eye on your impressions, and never fall asleep. It is no small thing that is being watched over, it equates with honesty, trustworthiness and stability. It is freedom from passion, grief, fear and consternation - it is freedom itself.
 What are you going to get when you trade your freedom away? Check to see what your proud new possessions will be worth.
-Epictetus, Discourses, Book IV