The moment you stop working out for your physical appearance you'll become more motivated.
When exercise is all about the way you look, and you fall short of your expectations a few times, you end up just giving up.
Instead of focusing on bigger, more elusive goals (hey, six-pack abs), try setting MICRO GOALS, that'll help you celebrate smaller victories along the way, like losing 2% of your body weight, nailing a push-up for the FIRST time or running 1/2 mile WITHOUT stopping.
You should feel amazing about these accomplishments and you should tell someone, and be proud and loud!!
Now, I'm not saying that you shouldn't have big goals as well, but the celebration of the small ones will make the journey towards them easier and more enjoyable. Next time you workout keep this in mind and remember that one "on your knees" push up is way better than no push ups at all!
See you guy soon!