I hear very often this theory that "it just doesn't work".
To be fair, I had also believed this for many years.
However, all the people who claim that "it just doesn't work", have never made any serious attempt to do "it", so they cannot know whether it does work or not.
I have been obese for more than a decade, during which I have made several attempts to lose weight, which have all failed, because they were not done in the right manner.
Then I have made a final attempt using the correct method, and I have lost about 35% of my initial body weight during about ten months, at a steady rate between 100 g and 150 g per day, i.e. about 1 kg per week.
This was more than 10 years ago and since then I have kept a constant weight. Because I have done this once, now I can control my weight and have any weight I want, even if I gain weight extremely easily. It is enough to eat one day like I was eating when I was obese to gain enough weight to require a week of weight losing diet to go back to the desired weight.
The rules for losing weight and maintaining the weight are very simple, but they must be observed and those who claim that "it doesn't work" never try to observe the rules, so it is entirely predictable that it cannot work for them.
First, it should be obvious that after losing weight one must eat differently as before, otherwise weight will be gained until reaching again the original weight.
To be able to control the weight, anyone who is or has been obese must stop eating until they feel satiated. At each meal, one must plan before beginning to eat how much to eat and then eat only the amount planned, never more than that. One must eat a fixed number of meals per day (preferably few, e.g. only two meals per day should be enough for an adult who has a sedentary lifestyle) and never eat between meals any kind of snacks or drink any sweet of fatty beverages. Between meals, only water or beverages without any calories (e.g. unsweetened herbal teas or tea or coffee) are acceptable intakes.
While losing weight, the most important thing is to weigh oneself every day with precise digital scales (with a resolution of 100 grams or less), at the same hour and in the same physiological conditions, i.e. in the same order with respect to meals and relieving oneself.
Whenever the weight is not less than the previous day, then the quantity of food planned for the current day must be diminished in comparison with the previous day. At the very beginning of losing weight there may be a delay, e.g. of a week or so between starting to eat less every day until the weight begins to decrease, but eventually it is possible to reach a steady state of a constant rate of losing weight per day.
When diminishing the amount of eaten food, only the carbohydrates and the non-essential fats must be reduced. The amount of proteins, essential fatty acids, vitamins and minerals must remain normal. To achieve this, one must eat a source of pure proteins, for example turkey breast or chicken breast or some kind of protein powders, so that eating enough proteins contributes only a minimum amount of calories. The rest of the nutrients can be provided mostly by non-starchy vegetables and perhaps by some supplements like fish oil. One could also eat almost anything that is not recommended, for instance chocolate, with the condition that the quantity is negligible, which can normally be achieved only when such treats are not eaten every day, but e.g. only once or twice per week.
These rules are simple and anyone who follows them will lose as much weight as desired. Obviously, this is easier said than done, because for the entire duration of the weight-losing diet one will be permanently hungry and one would tend to think about food and it will be difficult to resist temptations, so it is better to not keep in the house any kind of food that can be eaten immediately, without requiring some kind of preparation. Unfortunately, this is unavoidable and it is the price that must be paid. After the first few weeks, the hunger sensation diminishes in intensity and it always disappears for a few hours whenever you find some work to do that captures your attention.
As long as you do not want to follow such rules, you will not lose weight, but that is because you do not want to do it, not because it does not work.
Not wanting to do it is a valid reason, because one may abhor more the feeling of hunger during many months than being obese, but this decision must be described correctly and not be justified by the false claim that "it doesn't work". At least in my case, the improvement in my health and in what I was able to do (e.g. before losing weight climbing a few stairs would make me tired and sweaty) has made worthwhile any displeasure felt during losing weight and I have been very happy to have achieved that.