If we have a good heart, we experience much happiness and relaxation. We have no reason to feel angry or jealous and we have a very happy mind. When we speak, sweet words come out. Even our face is happy and smiling. At night we go to bed with a happy mind and have a very comfortable sleep, without any worries.
Otherwise, if we live our life with a very selfish, ungenerous mind, we think about nothing else except me, me, me: "When will I be happy? When will I be free from these problems?" If our attitude is like this, jealousy and anger arise easily, strongly and repeatedly, so we experience much unhappiness in our life, many ups-and-downs. During the day we have a cold heart and at night we even go to bed with a cold heart and unhappy mind."