Equanimity is the inner condition of a person of wisdom. A short Hindu story reveals the truth.
Once King Janaka's palace caught fire. King Janaka was a man of the highest wisdom. He was a man of inner poise. King Janaka witnessed his palace being burnt down without any disturbance, while people around lamented desperately about it.
The other part of the story also talks about a group of sadhus or monks who lived near the palace. When the raging fire spread furiously, the monks in the neighbourhood, scooted with their bare minimums like their, water pots, sticks etc.
Thus equanimity with inner poise is the nature of the man of true wisdom. He stands firm without the slightest swerve in loss and gain. This is termed as Sthitha Pragna, in Vedanta, the goal to be reached.