The Discipline of Assent is a very important discipline to develop. It is mental work. It is looking at things from a very rudimentary level. The goal is for you to observe "things" and "events" without consciously forming an opinion of them. This allows you to then think about what is an appropriate response in the context of "what virtue can I exercise given this thing or event?" You have to give yourself a change to re-act reasonably, which means developing a "pause" between observing a thing or event and your reasoned reaction to it.
Epictetus gives examples.
Observing that someone has died and that that event is out of their control.
Observing that someone has lost their inheritance and that that event is out of their control. Similarly, if it were you who lost your inheritance and then recognizing that that event is out of your control, is all you should do when exercising the discipline of assent.
Observing that someone has been condemned by Caesar or some authority figure and acknowledging that this event is out of their control ... full stop: that is the discipline of assent.
If, however, these events happen to someone or you, and that someone or you is disturbed by them - being disturbed by this is in your control and by being disturbed by them is failure on their part or your part.
However, if someone endures or you endure those events nobly and undisturbed - this is also in your control and is a success on their part or your part. In this case, you have exercised a virtue as a reaction to some event or thing out of your control. This is what Marcus meant when he said, "So in all future events which might induce sadness remember to call on this principle: 'this is no misfortune, but to bear it true to yourself is good fortune.'" (Meditations 4.49).
"If we adopt this habit, we'll make progress," says Epictetus (v. 4, p. 159).
The Universe/Zeus/God has given each of us "the ability to endure things, and has made [us] noble-minded, because he has prevented these things from being evils, because he has made it possible for [us] to suffer them and still be happy" (v. 6, p. 160).
Truly, we can choose the best, most virtuous reaction in any circumstance, but it takes mental toughness and discipline.