Everything has a cycle.
Birth and death are cycles very similar to the cycle a flower has from seed to blossom to withering. Each cycle of our life invites us to blossom in new ways. Understanding this lets us move through our own cycles with greater ease and less resistance. It defies the laws of nature to only be in one phase forever, and when we think that life should be different from the way it is, we suffer.
Sunrises and sunsets are great examples, as well. There is always a newness (or birth) with which we can see our experience. Sunsets represent the death of our day and the opportunity to experience the cycle all over again the next day. Both sunrises and sunsets are equally beautiful and ways that we can remember to honor the cycles of our own unique experiences.
Even the breath cycle of inspiration and expiration reminds us that one cannot exist without the other in its wholeness.
This is also true of mental, emotional, and physical body states of being. Discomfort, pain, acute illness, dis-ease and disease are all ways we can allow a death and a birth to take place while connecting with the certainty that all of life is a cycle and an invitation of renewal.