Your happiness depends on your getting the things you desire, on the things you value most in life, on your idea of good and bad. Not only happiness but other emotions too depend on our values. The belief that it is good to have stuff like a car, or a house, or lots of money, or fame, will make you happy only when you get those things, but if you don’t have them, you will be unhappy, wretched, miserable.

If something threatens those things, you will be angry. When you see someone who has those things, you will be jealous. If you are not certain whether you will get those things, you will be anxious. And even if you get them, you will always live with a fear that those things might be taken away from you.

Value externals, and you will be inclined to do anything and everything to get them, and so, it is possible that your actions will be vicious, shameful, wrong. All of this takes place when a person desires and values externals, which are outside their control.

But it is when you understand what is truly worth valuing, that happiness, and all other emotions, come under your control.

Let me explain.

Things that we should truly value, as the Stoics say, are acting virtuously, justly, courageously, with self-control, doing what the world requires from you – your duty.

It is obviously better to have power over your own self than on the whole world, to have a good character than all the money, fame, and fortune in the world, to be free than a slave, to be virtuous than vicious, to be wise than ignorant, and to always be cheerful than unhappy.

All these things, you can attain only when you put virtue above everything else; and recognize it as the only good, ignorance as the only evil, and everything else as neither good nor bad but indifferent. Once you do that, you start acting the way you should. And because what you desire now is to act virtuously, you can always get what you desire.

And, above all, you will be happy whenever you act in line with your principles. And so, you can always be happy, for it is in your own power to act the right way.

There is one road to peace and happiness (keep the thought near by morning, noon and night): renunciation of externals; regarding nothing as your own; handing over everything to fortune and the deity.

Epictetus, Discourses IV.4