I'd say that for me a few of my motivations are as follows:
feeling better, sleeping better, aching less (after the initial soreness once you start a new routine), seeing the 500 calories I have burned off on the bike/treadmill, having my clothes fit more loosely, retaining less water, feeling more motivated to stick to a healthy eating plan (I don't want to "undo" all the hard work I've done just for the fleeting pleasure of eating!), my health and intending to live to be a very old granny, to set a good example for my daughter, to reduce risks of several life-threatening diseases that being overfat predispose me to, to enjoy sex more freely and be more comfortable with my body in general and to be as vibrantly attractive as I used to be!
I remind myself of all these things to motivate me to workout and eat well whenever I feel like I can't go on.
The motvations for you will vary depending on your goals and where you are at in your life right now. Best of luck and you can do it. Just decide that you are worth taking care of and then do it!