Equanimity is an ability to not be affected by external phenomena.
Somebody with a well developed sense of it doesn’t get mad after getting cut off in traffic nor gets too excited after winning a prize.
Somebody with a really well developed sense of equanimity is basically always the same. He or she doesn’t change in one scenario or the next, in front of this person or the other.
Monks retreat from the world to build a kind of equanimity muscle. It’s necessary to remove yourself, practically, from all the various worldy triggers so that when you resume activity in the world, you can be left unaffected.
As soon as you get worked up, you get thrown into your personal self that feels the need to fight, struggle, make things right and the like. For the most part, it’s not a place we want to be in.
We can get caught there, getting tossed about by each crashing wave.
It’s not so much about defeating each wave but transcending the whole ocean and game altogether.
And that requires inordinate amounts of bravery to let go of a great many conventional truths.