01
The idea
Desire and aversion are treated by the Stoics as one faculty pointing two ways: reaching towards and pulling away from. Both create exposure, because both make your state depend on whether the world complies.
The instruction is not to stop wanting. It is to notice the difference between wanting a thing and requiring it — between "I will pursue this with everything" and "I cannot be all right without this". The first is ambition. The second is a hostage arrangement.
Epictetus is unusually blunt with beginners here: restrict desire almost entirely at first, aim aversion only at what is genuinely up to you, and let everything else be selected rather than required. It is a training instruction, not a permanent state.
02
Why this matters
Requirements are the mechanism by which capable people become fragile. Someone who requires the promotion, the reply, the recognition, the result is running a life whose stability is decided in other people's meetings.
It also degrades performance in the thing itself. Requiring the outcome makes you worse at the process — tighter, more defensive, less able to take the risks that produce the outcome.
And it is the difference between a setback and a crisis. The same event lands as an inconvenience or as a collapse depending entirely on which verb you had been using.