Question: You said that since the basis of human nature is egoism, happiness is possible only in the middle line. Could you explain this?
Answer: The middle line is a state where our egoistic desires, called the “left line” are balanced by the altruistic desires of the “right line,” and we work in harmony between them.
In other words, our egoism constantly helps us to work in bestowal and love of others. Then it really becomes fulfilled.
From the Kabbalah Lesson in Russian 12/11/16