There can be many mental and emotional barriers to getting in better shape. Some are fairly extreme and beyond the scope of this guide, such as anorexia or bulimia. But the ones that get most people in trouble are very simple, and are generally not that hard to overcome once they are recognized.
The most important thing is not the specifics of your program or the details of your diet (though those are obviously important), but how you look at the situation. I don't mean in the sense that your mind is more powerful than what you do in the gym, although you'll need to have some self-discipline and commitment for obvious reasons. The main problem is that most people look at fitness in a completely wrong way, and that's why they flunk, not because it has to be so hard in and of itself. What I mean is, you can't look at diet or exercise as a short-term ordeal that ends at some point when you aren't out of shape anymore. You need to look at them as long-term lifestyle changes. That sounds kind of scary, but is actually not a big deal when you think about it.
Consider this: when people start dieting and exercise, they are often extremists about it. They try to work out 2 times a day 7 days a week, or go on some crazy diet where they eat 500 calories composed entirely of herbal tea and tree bark. They hurt themselves or get sick or just hate life generally, and they fail. Then they get discouraged and get fat and out of shape again.
Was that a failure of willpower? Sort of, but the main problem is that the whole approach is wrong. You don't get in shape by killing yourself. You get in shape, and more importantly stay in shape, by accumulating significant, but livable, improvements to your lifestyle over time, and building on that. Not by going through some horrible ordeal requiring Olympian willpower.
Eating healthy has to just become how you eat most of the time. Exercise has to become a habitual thing you do every day or two, like mowing the lawn or taking out the trash. If you do just a little better all the time, but really stick to it, you can accumulate big gains very fast, and improve upon them over the long term. And once you start seeing improvements without having to kill yourself, it becomes very easy to keep on improving.
Another thing to consider is that many people find it hard to get into the shape they want because they have bad habits, especially when it comes to diet. Some of these are obvious, but many of them are not. Education about diet and exercise is very spotty, and the media (and even fitness magazines) often report nonsense that just adds to the confusion. Part of the purpose of this guide is to educate you enough to be able to identify your bad habits in the first place, and not just stop them, but replace them with habits that are positive. Habits are hard to break, but the rewards for replacing bad habits with good ones are immense and long-lasting.
-Liam Rosen, Spartan for life...