1. People often go on diets that are not sustainable. Eventually, after enough deprivation, it becomes too difficult and the desire for food overcomes them. Soon enough, they go back to their old eating habits.
2. People think that losing weight is the hard part, and maintenance is the easy part. They therefore devote a lot of time and energy into losing weight, but not into keeping the weight off. Maintenance requires at least as much time and energy as weight loss.
3. A diet is temporary. Depriving yourself temporarily is manageable. Maintenance is forever. Even though on a day to day basis maintenance requires less deprivation than dieting, forever is a very long time.
4. During a diet there are certain things motivating you that will not be there for you during maintenance. a: The excitement of having recently started a diet. b: The thrill of the scale saying you lost weight and your clothing getting looser. c: Assistance, support, and encouragement from family and friends. d: The vivid memory of how unpleasant it was to be overweight.
5. Challenges come up during maintenance (and during the late stages of dieting) that rarely come up when you start the diet (i.e. stressful experiences, travel, an injury, yomim tovim, etc.) Why don't these challenges come up during the diet? Because you, like everyone else who ever went on a diet, waited for a "perfect storm" to start your diet. You waited for the right situation where you were both highly motivated and in a good position to start your diet. For example - people don't start a diet BEFORE Succos.
6. On maintenance you need to have a lot more knowledge about nutrition and dieting. You will have to make judgment calls, and know exactly what each food choice will do to your body. On a diet almost everything is off limits so you don't need as much knowledge.
7. During maintenance you do not have to be as strict as you were during the diet. However, you may not be nearly as lax as you were before the diet. People are good at being extremely good or extremely bad, but not at finding a balance and sticking to it. The consistency necessary to change one's lifestyle is not developed on a diet, it's developed during maintenance.