The most important step in letting go is realizing that nothing has intrinsic value — nothing is good or bad. In our daily lives, how we motivate ourselves is to think “some steak would be good right now” or “it sure would be good to get on holiday”; this is a horrific mistake that plays havoc with our emotions. We seek things passionately, and experience brief elation when we get them, but this soon fades — and if we fail to get them, we are downhearted. Likewise, we think “it would be bad if my car broke down” or “it would be bad if this girl rejects me” — this brings about fear, and again depression if these things come to pass.
Now, if we were to eliminate all forms of evaluation, according to Stoic psychology, we would simply die, because we would have no motivation to do anything at all. Instead of elimination, the key is transformation from good and bad into preferred and rejected (at a basic level, pretty much all the things you’d see as “good” are preferred). These things are rationally and dispassionately pursued and avoided respectively, but emotions are absolutely out of the question. It is a mistake to be elated if you achieve something that is preferred; likewise it is a mistake to feel sadness if something rejected comes to pass. You retain evaluative judgements as guidelines for making decisions; nothing more.
Virtue is the condition of following this rule: rationally selecting the preferred and disselecting the rejected. It is virtue — making the right decisions — that will become the basis of your eudaimonia (happiness; fulfilment), not the results of this. Good and evil, happiness and sadness, are in the will. When it comes to externals, in the words of Marcus Aurelius, “remove the ‘I am hurt’, and you remove the hurt”.
In everything that pleases your soul, or supplies a want, or that you are fond of, remember to add this to your thoughts: what is the nature of this thing? If you are fond of a vase, say that it is a vase that you like, and nothing more — for when it has been broken you will not be disturbed. If you are kissing your child or wife, say that it is a human being whom you are kissing and nothing more — for when the wife or child dies, you will not be disturbed.
Epictetus, Enchiridion III
A big part of Stoicism is regarding yourself as a sovereign will: you are entirely in control of it, and everything outside of it, and whatever happens to these external things (including the body) is not your concern when it comes to happiness.
“Tell me the secret which you possess.” I will not, for this is in my power. “But I will put you in chains.” Man, what are you talking about? Me, in chains? You may fetter my leg, but my will not even Zeus himself can overpower. “I will throw you into prison.” My poor body, you mean. “I will cut your head off.” When then have I told you that my head alone cannot be cut off?
A dialogue between a hypothetical oppressor and Epictetus from Epictetus’ Discourses.