While your character is formed by your circumstances, your desires can shape those circumstances. The one thing over which you have absolute control is your own thoughts. It is this that puts you in a position to control your own destiny.
Nature is constantly at work around you. Character and destiny are her handiwork. She gives you love and hate, jealousy and reverence. You have the power to choose which impulse you follow.
At any time you can decide to alter the course of your life. No one can ever take that away from you. You can do what you want to do and be who you want to be.
Your greatest power is the power to choose.