If we think only of ourselves, forget about other people, then our minds occupy very small area. Inside that small area, even tiny problem appears very big. But the moment you develop a sense of concern for others, you realize that, just like ourselves, they also want happiness; they also want satisfaction. When you have this sense of concern, your mind automatically widens. At this point, your own problems, even big problems, will not be so significant. The result? Big increase in peace of mind. So, if you think only of yourself, only your own happiness, the result is actually less happiness. You get more anxiety, more fear.
~Dalai Lama XIV, The Wisdom of Forgiveness