Epictetus tells us here that we must stop worrying about things such as losing our material possessions in the future or that our slave will turn out bad if we don't discipline him. "It is better to die of hunger free of grief and apprehension than to live affluent and uneasy. Better that your slave should be bad than you unhappy."
Epictetus tells us to start small and practice not worrying about such things. For the price of something spilled, like wine or oil, we are to remember that we are buying peace and tranquility. When dealing with people we must always remember that they could ignore us or not follow our instructions. The person who has ignored you, even if they owe you, "is not worth entrusting with your peace of mind."
What is the problem with worrying about losing our future material possessions? How could it be better to die of hunger? For the Stoics, material possessions were outside of our control. As were other people. So we cannot expect to make progress in what we control if our time is spent foolishly trying to control what we cannot control. Epictetus's position then is not simply that we should not care as much about things. He wants us to not care about indifferent things so that we can make progress in what truly matters: virtue.
Whether or not we agree with Epictetus that virtue is the only good and therefore we should not care about anything else, many of us probably care far too much about things that don't really matter. Our culture through advertising and the wiles of the internet encourages us to focus on having the best and finding the best and procuring the best. We are often not worried that we might become destitute but that we might miss out on a more perfect experience. Heaven forbid the color reproduction on our new flat screen isn't as good as another persons! Or that our recipe for pasta salad dressing isn't as sublime as another's!
Is our peace of mind and tranquility worth letting things go? Ninety five percent of the time, yes. Don't stress about spilled milk or cranky co-workers. Buy your tranquility and peace of mind everyday this way. Don't worry that you will miss something important if you stop worrying about everything. When something is important you will know. Mark the truly important stuff like paying the bills and renewing the insurance on the calendar. Stop worrying about the rest. The alternative is to live without peace in an attempt to divert a disaster that might always be coming. Instead, start with small things and buy your tranquility now.