Why are volunteers willing to work for free?

In fact, everyone's life is not easy, economic pressure, family pressure, they will also encounter many bitter fruits in their own workplace; Seeing social injustice, they will also complain about society, but the biggest difference is that they will put it into action later, hoping to bring about a little change through their own little actions. "Someone has to do something, always saying that I am tired and others are tired. Just move. " When a volunteer was chatting with us, the joke he told was particularly memorable.