You develop equanimity when you need to see things that you don’t yet understand. When you understand, sometimes equanimity is still appropriate, and sometimes you need to do something more forceful to deal with the problem at hand.

"And equanimity, too, is something you have to will — the ability to stay unperturbed with the things you like and the things you don’t like; not getting excited when things go well, not getting depressed when they don’t. In other words, you train yourself to have a certain amount of independence. Discernment is needed to perfect and understand this quality, and the equanimity helps foster the discernment, allowing you to see things more clearly, as well. The two qualities go hand-in-hand. There are times in the meditation where you do simply have to sit and watch. Some of your defilements really will go away just when you watch them — but not all of them. One of the points of developing equanimity is so you begin to see where the difference lies.

So the Buddha is not recommending a blanket passivity here. He’s telling you to develop equanimity when it’s appropriate. You develop equanimity when you need to see things that you don’t yet understand. When you understand, sometimes equanimity is still appropriate, and sometimes you need to do something more forceful to deal with the problem at hand."

~ Thanissaro Bhikkhu "The Will to Awaken"