When one does not understand death, life can be very confusing. If our body really belonged to us, it would obey our commands. If we say, "Don't get old," or "I forbid you to get sick," does it obey us? No, it takes no notice. We only rent this house, not own it. If we think it belongs to us, we will suffer when we have to leave it. But in reality, there is no such thing as a permanent self, nothing solid or unchanging that we can hold on to.
Buddha made a distinction between ultimate truth and conventional truth. The idea of a self is merely a concept, a convention-American, Thai, teacher, student, all are conventions. Ultimately no one exists, only earth, fire, water, and air-elements that have combined temporarily. We call the body a person, my self, but ultimately there is no me, there is only anatta, not-self. To understand not-self, you have to meditate. If you only intellectualize, your head will explode. Once you understand not-self in your heart, the burden of life will be lifted. Your family life, your work, everything will be much easier. When you see beyond self, you no longer cling to happiness, and when you no longer cling to happiness, you can begin to be truly happy.
The above wisdom from the Thai forest monk Ajahn Chah is taken from a wonderful book by Jack Kornfield & Paul Breiter, which can be read about here Review: A Still Forest Pool.