Cassian’s advice on anger
. . . When we are angry with others we should not seek solitude on the grounds that there, at least, no one will provoke us to anger, and that in solitude the virtue of long-suffering can easily be acquired. Our desire to leave our brethren is because of our pride, and because we do not wish to blame ourselves and ascribe to our own laxity the cause of our unruliness. So long as we assign the causes for our weaknesses to others, we cannot attain perfection in long-suffering.
Self-reform and peace are not achieved through the patience which others show us, but through our own long-suffering towards our neighbor. When we try to escape the struggle for long-suffering by retreating into solitude, those unhealed passions we take there with us are merely hidden, not erased; for unless our passions are first purged, solitude and withdrawal from the world not only foster them but also keep them concealed, no longer allowing us to perceive what passion it is that enslaves us. On the contrary, they impose on us an illusion of virtue and persuade us to believe that we have achieved long-suffering and humility, because there is no one present to provoke and test us. But as soon as something happens which does arouse and challenge us, our hidden and previously unnoticed passions immediately break out like uncontrolled horses that have long been kept unexercised and idle, dragging their driver all the more violently and wildly to destruction. Our passions grow fiercer when left idle through lack of contact with other people. Even that shadow of patience and long-suffering which we thought we possessed while we mixed with our brethren is lost in our isolation through not being exercised. Poisonous creatures that live quietly in their lairs in the desert display their fury only when they detect someone approaching; and likewise passion-filled men, who live quietly not because of their virtuous disposition but because of their solitude, spit forth their venom whenever someone approaches and provokes them. This is why those seeking perfect gentleness must make every effort to avoid anger not only towards men, but also towards animals and even inanimate objects. [...]
The final cure for this sickness is to realize that we must not become angry for any reason whatsoever, whether just or unjust. When the demon of anger has darkened our mind, we are left neither with the light of discrimination, nor the assurance of true judgment, nor the guidance of righteousness, and our soul cannot become the temple of the Holy Spirit. Finally, we should always bear in mind our own ignorance of the time of our death, keeping ourselves from anger and recognizing that neither self-restraint nor the renunciation of all material things, nor fasting and vigils, are of any benefit if we are found guilty at the last judgment because we are the slaves of anger and hatred.