Thanissaro Bhikkhu on Equanimity

"[An awakened person] feels sympathy for others and seeks their well-being, experiencing a sense of satisfaction when they respond to [his/her] teachings, but otherwise [he/she] stays equanimous, untroubled, mindful, and alert. This passage shows that the even-mindedness of a fully awakened person is an attitude not of cold indifference, but rather of mental imperturbability. Such a person has found true happiness and would like others to share that happiness as well, but that happiness is not dependent on how others respond. This is the ideal state of mind for a person who truly works for the benefit of the world." ~ Thanissaro Bhikkhu "The Wings to Awakening"

"When, while you’re trying to develop compassion and empathetic joy, you run across cases where you can’t help the other person, either to become happy or to maintain happiness, that’s when you have to develop equanimity. This is the equanimity of a good doctor who realizes that he can’t solve all the cases in the world. But if he lets his heart get broken over all the cases he can’t solve, he won’t have the energy to help the cases he might have been able to solve. So for the people who come to him and have the karma that allows him to help — and he himself has the karma that allows him to help them — he should think of that as a precious opportunity. It’s not always there. Make the most of it and don’t let yourself get distracted by things you can’t control or where you can’t be of help. Because, as I said, karma is complex. The combination of the patient’s karma to be in a position where he or she can be cured, and the doctor’s karmic connection with that patient: It doesn’t al

"We hear about awakened people who are extremely equanimous. But it’s not the case that the equanimity is the essence of their attainment. After all, the Buddha didn’t say nirvana is the ultimate equanimity. He said it’s the ultimate happiness. But the fact that awakened people have a basis for their happiness that doesn’t depend on conditions: That allows them to look at conditioned reality with a lot more equanimity. They’re not trying to feed on it anymore; they don’t need it for their happiness. So the equanimity is a byproduct." ~ Thanissaro Bhikkhu "Equanimity Isn't Everything"