With regards to losing weight and keeping it all, probably the most important thing isn't diet or exercise. It is motivation. When you can hold on to the motivated, you are able to meet up with your targets, become more in good physical shape, and stick to a healthier way of life.
Unfortunately, most of us have trouble staying motivated. Of course, it's not hard to decide to diet and exercise and stick to it for a few of weeks; but eventually, most of us get to a spot where we lose the focus of ours and give up.