Have you worked out and dieted your way to within eyesight of your goal, only to fall off the wagon? Getting back on can take time and introspection. If you don't understand why you fell off in the first place, fear may keep you from getting back on, and you'll regain all the weight you've lost.
When you're working hard, the question you need to ask yourself is "how hard is too much?" If you're working harder than you realize, you could be stopping your body from losing weight. Sometimes you need feedback from a heart-calorie monitor to help you get over a weight loss plateau.