When I was growing up and would struggle with not accomplishing what I wanted to, or not excelling the way I knew I was capable of, my mom would say something brilliant to me. She'd say, "When it matters enough to you, you will". Now, don't get me wrong, the little girl in me at the time did NOT see the brilliance of this statement! It was only with time (like so many things), that I truly understood.
We ALL have started down paths of health and fitness (some of us many paths), only to feel defeated and throw in the towel. To stay on track you need to discover why it matters to you. This why needs to go deeper than "I want to fit into a size___" or "I want to wear ____ at this occasion". These whys are fleeting. Find out WHY taking care of yourself matters on a deeper level and you will feel your commitment to you path grow.