Our souls or unique minds or our true inner identity is sovereign. But the body and senses will take over our purest freedom, if we are not careful. Therefore, it is imperative we exercise the discipline of assent in all matters that are external to the soul; else we slip into a type of bondage.
I'll follow Epictetus' examples.
If you choose to be angry, it is because you've abdicated your responsibility to choose your attitude. You've left the choice with your base instincts and with others who would trigger you.
The same goes for sex or other pleasures. "It is inevitable that continuous behavior of any one kind is going to instill new habits and tendencies while steadily confirming old ones" (verse 6).
If you see something you want (greed) but counter the first impression with reason "to alert you to the danger" then "the passion will abate and the mind will be restored to its former balance" (verse 8). And I think that word is very important: balance. We can all become imbalanced and if we don't restore our harmony, and instead yield to passion, the next time we are 'tipped' we will fall more easily and quickly. Then we lose control.
He gives an excellent visual: vice (the opposite of virtue, with virtue in the center and vice to the extreme on the left and the right) is like a blister or scar. The more you agitate it, the longer it will take to heal. You must allow them to heal well if you would not have the wounds open again.
Another excellent piece of advice from Epictetus: "Suppress the first impulse to be angry, then begin to count the days on which you don't get mad" (verse 12, emphasis added). I remember Jerry Seinfeld giving some advice about becoming successful. He described a "don't break the chain" habit, wherein he hangs up a big year-view calendar on his wall. And every day he created new material, he could put a big red "X" on that day. Then his goal was simply not to break the chain of red "X's" (link here). Whether building a habit of doing something or a habit of not doing something, the idea is useful.
On a related note, Seneca advises a daily review at the end of the day; whereby you become the judge and the judged (see On Anger Book 3, 36). This is a good habit to develop.
Epictetus gives other related advice on developing habits
- "socialize with men of good character, in order to model your life on theirs."
- "don't let the force of the impression, when first it hits you, knock you off your feet; just say to it, 'Hold on a moment; let me see who are you and what you represent. Let me put you to the test."
The challenge of challenging impressions is perhaps the greatest "sport" - that of "training to face off against the most formidable of impressions" (verse 27). "It's a fight for autonomy, freedom, happiness and peace" (verse 28). But it is a worthy fight and challenge.