As kids we have a number of dreams about what we want to become when we grow up. As we do (grow up) those dreams change and modify themselves into something concrete. Slowly we come to terms with the reality and the unrealistic ones gets dropped off from our arsenal and the realistic ones becomes the point of our focus.
Some we are able to achieve and some not. Wheras self concept is about trying to become the person you want to be, self actualization is about trying to come to terms with the person you are now. This is the key to understand where you stand in life currently and where you want to be.