My observation is that the fat people who become "normal" size and maintain that size for more than just a few years, manage to do this through doing the hard work it takes to continually and consistently oppose the natural physiological desires of their "reduced obese" bodies.

Rather than allow their bodies to tell them how to eat, they use their minds to overrule those bodies and consciously choose to eat food containing far less calories than their individual body desires.  Forever … one-day-at-a-time. 
It is possible, but it isn't easy.  
See Running Down the Up Escalator.

First, let me clarify that my definition of a "fat" or "obese" or "reduced obese" person is not someone who merely hangs somewhere around their BMI Obesity border. Meeting that criteria requires a person to put in more than two or three years at a weight of … at least …. 20 to 50 pounds above their BMI Obesity border. To me, those who fail to meet that requirement are merely "overweight", a condition that is often temporary for them. Although many of these people term themselves as "fat" or previously obese, in general, they appear to have a very limited understanding of true obesity or the fat condition.

An overweight person tends to think that because they went on their first diet and easily lost and kept off 10 or 20 lbs, then an obese person, on their 50th diet can do the same thing for a longer time and lose and keep off 100+ lbs. This attitude is easily seen within the numerous online diet forums that are full of overweight or formerly overweight people who are eager to offer copious advice and personal judgments along these lines to people who are obese or reduced obese.
This unequal comparison … apples to oranges … often confuses people who are truly obese or "reduced" obese and frequently results in negative self-judgments which are just wrong.

So, applying this clarification, There are psychological desires (of the mind), and physiological desires (of the body). What does it take to continually and consistently use one's mind to oppose the natural physiological desires of one's body? Is the ongoing difficulty of opposing those desires worth the effort that it takes to be "normal" weight?

This is a Judgment call that depends   
on the severity of the individual's mental pain which is caused by the culture's fat-bias, and the severity of the individual's physical pain which is caused by denying to one's own obese, or reduced obese body, the food substances which that body believes it needs for survival. 

We must each decide this for ourselves. Thus far, for me personally, the balance tilts toward accepting the physical pain to avoid the mental pain. However, my personal dieting ...

Looking for Progress,
because there's NO Perfection

Who Cares if 3,500 Calories Don't Make a Real Life Pound?
                      by Dr. Yoni Fredhoff, M.D. 12/12/13 @weightymatters

If there's a more painful discussion in nutrition and obesity these days beyond the one that circles the question, "Do 3,500 calories really make up a pound?", I don't know what it is.

So here are some truths.

• People are not walking math formulas whereby if they have 3,500 more or less calories than they burn they'll gain or lose a pound.
  
• 3,500 calories of one food or type of food will likely have a different impact on health, hunger, thermic effect, and weight than 3,500 calories of another food or type of food.
  
• Different people have different caloric efficiencies whereby they are seemingly able to extract more calories from food or reserves than others and lose weight with more difficulty (and gain with greater ease).
  
• And yet here's the only truth that matters.

From a weight management perspective, the currency of weight is calories. While exchange rates undoubtedly do vary between foods and between individuals, you'll always need your own personal deficit to lose, and surplus to gain.

All other discussion, while certainly academically interesting, given that there are No Other Alternate Measures Available to track, or tests to determine individual responses to different calorie sources, serves to foment confusion.

If weight's your concern, more important than anything else is finding a life that you enjoy that contains fewer calories than before. Getting stuck in the minutia of what type of calories may lead to an every so slightly faster or greater loss, rather than truly crafting a life that's enjoyable (and hence sustainable), might help in the short run, but will almost certainly defeat you in the long.

I agree with the following illustration used by Dr. Sharma, M.D. a medical specialist who deals with obesity issues.

Weight Management is like a rubber band.

Weight Loss is pulling on the rubber band.

Weight Maintenance is KEEP pulling on the rubber band.

The individual question regarding our own Weight Management is: 

“HOW MUCH CAN WE PULL ... AND KEEP PULLING?"

This is analogy describes my own lifetime experience. That Truth is especially applicable to my past 7 years of maintenance within the “normal” BMI range, after years of yo-yo dieting up to a high of 271 lbs at 5’0” tall”, with a subsequent total weight loss of 156 lbs. To better visualize this amount, this number was 58% of my TOTAL body weight, which is a similar total amount lost by many of the winners of the “Biggest Loser” television show.

Rubber bands come in different sizes and strength. So do the bodies of people. It naturally follows that the more weight a person loses, the more the "tension of the rubber band".  This is why it usually takes far less effort for someone who loses 10 lbs to maintain that weight-loss, than someone who loses 100 lbs. 

Bodies appear to have a Set Point, which is like a rubber band in it's natural state .. unstretched.  However, it is clear that weight-gain will drive the body's natural Set Point higher. Although most people hope and pray that weight-loss will re-set that altered Set Point back to a lower number, all available evidence indicates that this is a one-way--upward-only--survival path.  Click link for more information about Set Point.

   I’ve been reading a great many things written by Dr. Sharma. At this point, I have a lot of respect for his expertise and point of view.

I like the fact that Dr. Sharma believes that people need to stop beating themselves up for a lack of motivation, and understand that there are very good reasons why they struggle with their weight. He says: