In chapter four Epictetus encourages us to visualize what we can expect before we undertake an action. He uses the example of going to the bathhouse. Before we go to the bathhouse we should remember what the environment is like, so that we will not be caught off guard when something happens that goes against our plan in some way. We may want a quiet bath, but it is outside of our control. We must remember that we always have another goal: to keep our wills in line with nature. Thus, even if our other actions are thwarted in some way, we still have a goal that we can obtain.
This of course is easier to say than to do. But Epictetus encourages us to do it with every act. In anything we do we cannot control how external circumstances will unfold, but we can always control how we will respond to whatever happens. Fighting against what we cannot control and allowing ours emotions to be controlled by circumstance will always lead to disappointment. Instead, decide ahead of time when you know things might go sideways that you will keep your will in line with nature.