This video is a great visual illustration of how making mistakes or cheating on your diet can affect your results. A lot of people think, "I work out, I can afford to eat some fries, or drink a double whip white chocolate mocha."
Think about what you're doing. I know I'm not the perfect example of this. I've been struggling a lot with this lately. I'm not gaining any weight/fat. However my frequent straying from my diet has stalled my results.
Check out this video. Why I don't agree with the sentiment that Cardio isn't important. Its critical for your overall health. However, why do all the work if you're going to waste all your back breaking hard work and effort with your diet.