One persons success at losing weight, getting fitter or improving their health, using a particular diet or exercise regime, does not mean it will work for the next person.
If you consider the "Triangle of Health & Fitness" then all three sides must be in balance to achieve one's optimum health, fitness & weight.
Knowing how food, lifestyle & environment impact upon our health, fitness & weight, is of major importance in achieving long term success.
Realism & Practicality
Understanding what you can realistically achieve, and how you are going to get there, is an often overlooked aspect of many diets and fitness regimes.