an excerpt from ancientsbest.co.nz which I love:
As an analogy, we can compare Yoga to that of the ocean; as a vast body of water; endless and eternal. In the ocean all is one and never separate though there are often waves. We can compare these waves to the human birth and the ego that makes us feel we are separate to others. As soon as we feel this separation we suffer all the limitations and fear of associating ourselves with the individualised body and mind, of being the wave and not the ocean. There are many waves but they are never separate from the ocean, and it is only due to karma/maya we (the body and mind) assume the form of waves.