I believe we are born in human form to grow and learn. As we learn we grow and evolve. If we fail the lesson we are recycled and have to be reborn to try and learn it over and over until we get it.
The Master always talked to me about moderation in all walks of life. Not too much Yin or too much Yang they would say you have to have balance in your life to be healthy and live a long life without pain and suffering.