Equanimity is a protection from what is called the eight worldly winds-praise and blame, success and failure, pleasure and pain, fame and disrepute.
Our moods tend to swing and can be quite extreme, like pendulum swinging from one end to another. Equanimity is to reduce the oscillations and maintain a peaceful frame of mind.
A group was engaged in a singing practice. A carpenter was setting the stage. Every time the carpenter made some noise, the choir leader looked at the carpenter silently indicating that he was disturbing their practice. This continued for a while and finally the carpenter told the leader, “Don’t worry, please continue your practice. It is not disturbing my work.” That was his level of equanimity.
The wise remain equanimous in all life situations, regardless of the joy or misery these situations bring forth. The mental framework of the wise does not oscillate amid the ebb and flow of life.