All the thoughts that are going on in your mind are not just random thoughts; they are all rooted in the past.
Your past is part of you, and it is always there to affect your present. And your 'present' is the past of your future. The future will be what you make of it.
If you want to change your life, you have to start with yourself. If you want to create something new in your life, first create it in your mind. If you want to change the world, start with yourself.