Our attaining the eudaimon ('happy') life requires that we judge things in the right way, for 'it is not events that trouble us, but our judgments of those events' (Epictetus, Handbook 5) (14).
The Three Disciplines establish activities in which the Stoic practitioner applies their Stoic principles; they are practical exercises "that when successfully followed are constitutive of the eudaimon ('happy') life which all rational beings are capable of attaining" (14).
There are three fields of study in which the man who is going to be good and excellent must first be trained. The first has to do with desires and aversions, that he may never fail to get what he desires, nor fall into what he avoids; the second with cases of choice and of refusal, and in general, with duty, that he may act in an orderly fashion, upon good reasons, and not carelessly; the third with avoidance of error and rashness in judgement, and, in general, about cases of assent (Epictetus, Discourses, 3.2.1-2, trans. W.A. Oldfather).