I have done some major head-scratching over the years, asking myself why some people achieve their goals and others do not. The answer finally came to me, and it was really quite simple: The ones that achieved their goals deeply believed they deserved to.
If you can't make fitness a true habit, maybe a better question is, at what point do you start craving exercise? When does it become something you look forward to enough to do regularly without putting up an internal fight?
If you think you get a better workout, or feel motivated to do a harder workout when you're listening to your favorite tunes, it's not your imagination. Recent research actually shows that people exert more effort and don't mind doing so when they're pumping to the jams.