Last updated December, 2019.
Everything changes, nothing is permanent: equanimity is a concept tied to this truth.
It is defined as "mental calmness, composure, and evenness of temper, especially in a difficult situation."
Why is equanimity important?
The way we normally treat thoughts, emotions, people, places, things (i.e., everything in life) is by labeling, categorizing, and judging them. This leads us to habitually react with desire for experience that gives rise to pleasant feelings, and aversion towards experience that gives rise to unpleasant feelings. This in turn, shapes (dictates) the decisions we make and the actions we take.
This process guides our life, and we tend to blindly follow it as we go through our days. Or, perhaps more accurate, we operate on autopilot, largely unaware as this process unfolds moment after moment, shaping "who we are" and "what we do."
Equanimity offers another path: adopt a neutral view of experience. Drop the labels and judgment, and see reality as it is - without the mental filters and constructs we usually place on top of it. This is the first step to disrupting the process described above.
Equanimity goes hand-in-hand with impermanence. It's difficult to apply equanimity if we don't realize that everything comes into being, exists for a time, and ceases. And, if we apply equanimity consistently, it will combat our minds' attempts to make everything permanent by continuously "grasping after" this and "pushing away" that.
Equanimity has another benefit: it helps end the self-imposed suffering (worry, anxiety, frustration, depression, et cetera) that comes from the process above (labeling, judging, and generally trying to control experience).
As Stoic philosophy tells us, it's not the situation that causes us problems, it's our thoughts about the situation. By applying equanimity, we'll find this isn't just an empty platitude. And, once we free up the time and energy previously spent on "mental gymnastics," we can use it to make more skillful decisions and take more skillful actions.
This quote from Gil Fronsadal nicely sums up the relationship between equanimity and impermanence:
Neither a thought nor an emotion, it is rather the steady conscious realization of reality's transience [impermanence]. Equanimity is the ground for wisdom and freedom.
Stop getting caught up in the stories running through your head.