You are the author of your story, and you play the prinicpal part. Once you understand this, you can begin to recognise life themes, and the roles that myth and archetypal characterisation play in shaping our life themes. From that point you can identify those people who have played the most influential roles in you life and can recognise the input they have made - and this is a vital part of shaping the story of your life and understanding the themes and patterns that have been consistent throughout that life.
This level of awareness is obviously important for anyone planning to write their life story, but it also helps in your consciousness of personal relationship patterns and therefore in the characterisation process you undertake every time you attempt to create fiction. The advice that you should 'write what you know' is fine, but first you need to recognise what you do know - and this book will help you on that voyage of discovery.