From Margaret R. Graver's Stoicism and Emotion:
"For emotions are `irrational': while they are going on, we find ourselves `blinded,' unable to prevent ourselves from doing things our calmer selves would not approve. It is, he says, "as if we had become different people from those who were previously conversing."
At the same time, in what seems a startling contradiction, Chrysippus also holds that emotions are in our power. His view of the causes of emotion is that of Zeno as reported by Cicero in the Posterior Academics; it is the standard Stoic position:
Whereas the ancients held that these emotions are natural and devoid of reason and placed desire in one part of the mind, reason in another, Zeno ... did not agree; he thought that the emotions are volitional and are experienced through a judgment of opinion.'
The language is that of moral responsibility: emotions are voluntarii or volitional; they are, as other sources put it, `up to us.' This language is not offered out of perversity or in ignorance of the recalcitrant nature of emotional experience. Chrysippus is actually quite pessimistic about the possibility of simply restraining oneself, for he holds that emotions tend to be unstoppable once they have begun. Nonetheless, he is prepared to assert that the recalcitrance of emotions can be explained satisfactorily within a moral psychology that counts affective responses as instances of voluntary action.
The position is in fact a coherent one. Chrysippus is able to make these bold claims because he has a clearly defined notion of what is required for something to be `up to us' or voluntary and a strong case for why the core instances of emotion satisfy that requirement. His explanation of moral responsibility is developed in the first instance without reference to those special or "hot" impulses which count as pathe: it is a matter of very broad philosophical significance, meant to supply a basis for praise and blame which does not violate the principle of universal causal determinism. But Chrysippus and other Stoics were also prepared to apply that explanation to emotional outbursts and their moral significance, taking due note of those features of emotional impulses which differentiate them from one's other conscious actions. The result is a sophisticated affective volitionalism which manages to combine intellectual seriousness, devoid of magical or mysterious elements, with sensitivity to the phenomena of our mental life. There are, to be sure, certain fairly obvious objections, based, as in similar modern discussions, on the nonsufficiency and/or nonnecessity of belief causes. But the Chrysippan analysis is able to resolve these objections without major modification.
The admission that morally significant responses can evade our control leaves us, as agents, in a difficult spot. We cannot prevent ourselves from doing certain things when we become upset, but all the same we cannot allege the strength of our emotions in order to excuse ourselves. This is a hard doctrine, yet if I read the evidence correctly, the Stoic founders were not inclined to soften it; rather, they issued it as a challenge. For helplessness is not the inevitable human condition, nor is it our natural condition; it is only the condition of persons who are not yet fully mature. To assume the full stature of our humanity would also be to enter a different realm of affective experience, one where strength of feeling does not have to mean loss of control. Although emotions as we presently experience them are not tame or easily managed, the affects of the wise carry them exactly where they wish to go. This is one reason why the attainment of wisdom is felt as liberation."
Margaret R. Graver. Stoicism and Emotion (p. 62). Kindle Edition.