Just as energy can be used for many different purposes, so can pure existence be experienced in relation to any phase of life—anger, hatred, or jealousy as well as love and beauty. Every human action must be carried on through the ego, which plays a role comparable to that of a pipe or channel through which energy is conducted for different uses. We usually think of the ego as a kind of constant, unchanging entity. In fact, however, it is simply a succession of physical and mental events or pressures that appear momentarily and as quickly pass away.
–Katsuki Sekida, from A Guide to Zen (New World Library