You can exercise all you want...if you eat like crap, you will not see the level of success that you would if you paired your hard work with healthy eating habits. I have seen it over and over again in myself. There have been times where I have let my diet slide (diet in the sense of what I eat, not an actual "I'm on a diet" kind of diet) but worked out hard, and seen absolutely NO movement on the scale. For weeks on end, even. When I was new at this, I was a little puzzled...how could I be working this hard and sweating like a pig, yet not losing any weight?! But once I was honest with myself (again, there's that damn honesty piece popping up), I realized that what I put in my mouth was not healthy or conducive to losing weight or getting fit. As soon as I started watching what I put in my mouth and concentrating on eating quality foods in decent quantities...the weight started coming off again.
So when you get stuck, make sure you take a good look at your habits - are you working your butt off at the gym, only to negate all that hard work with chinese take out, pizza, donuts and soda? Don't be surprised then, that you aren't seeing much progress. Even if you must take small steps towards a better diet, it's better than nothing. Keep working at matching your diet to your exercise, and success will come. You just can't give up, because these things take time. A whole lot of agonizing, frustrating time. Time that is worth it in the end!
REMEMBER: Your exercise is only as efficient as your diet allows it to be.