Eating less calories than losing is what makes one lose weight. This is why so many calorie-restricting diets are a success in the first few months of them.
Keeping the weight at lower levels is a different thing entirely. This is why so many calorie-restricting diets fail when people gradually abandon them.
Humans have a built-in sensor of satiety. If the sensor is signaling that they are hungry, they feel uncomfortable, and go looking for food, sooner or later. This can be suppressed by willpower, but it's taxing and distracting. This is why so many calorie-restricting diets get abandoned: the initial serving of willpower allocated to the self-restriction ends, and people want to proceed with their lives without having to fight the feeling of hunger most of the time. Between keeping a healthy weight and performing well on a demanding mental job they usually choose the latter. Whoever can lose weight on pure willpower is a hero; others can strive to emulate them, but should not assume they will be as successful.
So substances that help blunt or remove the feeling of not having eaten enough are important. Some of them are medical drugs (say, modafinil has this effect), some are household substances (like caffeine), some are real dangerously addictive drugs (like nicotine or cocaine). But there are mechanical sensors right in the stomach, which are harder to suppress with substances. This is where surgical means can and do help. Cutting a part of your stomach is now done via a very small incision in one's abdomen.
Morbid obesity is a disease, and should be treated as such. Shaming someone obese is like shaming someone with a broken leg: both painful and not helpful.