Equanimity is a fundamental skill for self-exploration and emotional intelligence. It is a deep and subtle concept frequently misunderstood and easily confused with suppression of feeling, apathy or inexpressiveness.
Equanimity comes from the Latin word aequus meaning balanced, and animus meaning spirit or internal state. As an initial step in understanding this concept, let's consider for a moment its opposite: what happens when a person loses internal balance.
In the physical world we say a person has lost balance if they fall to one side or another. In the same way a person loses internal balance if they fall into one or the other of the following contrasting reactions:
Between suppression on one side and identification on the other lies a third possibility, the balanced state of non-self-interference…equanimity.
Equanimity belies the adage that you cannot “have your cake and eat it too.”When you apply equanimity to unpleasant sensations, they flow more readily and as a result cause less suffering.
Psycho-spiritual Purification = (Pain x Equanimity) + (Pleasure x Equanimity)
Furthermore, when feelings are experienced with equanimity, they assure their proper function as motivators and directors of behavior as opposed to driving and distorting behavior. Thus equanimity plays a critical role in changing negative behaviors such as substance and alcohol abuse, compulsive eating, anger, violence, and so forth.
Equanimity involves non-interference with the natural flow of subjective sensation. Apathy implies indifference to the controllable outcome of objective events. Thus, although seemingly similar, equanimity and apathy are actually opposites. Equanimity frees up internal energy for responding to external situations. By definition, equanimity involves radical permission to feel and as such is the opposite of suppression. As far as external expression of feeling is concerned, internal equanimity gives one the freedom to externally express or not, depending on what is appropriate to the situation.
--Shinzen Young, from "What is Equanimity"