Body fat is simply stored energy (calories).
To lose fat, more calories need to be leaving your fat cells than entering them.
In other words, if calories out is greater than calories in, fat loss occurs. That is a fact.
For this reason, it seems only logical that "eating less and moving more" would cause weight loss. It works on both sides of the calorie equation.
However, this is really terrible advice for those with a serious weight problem. Most people who follow this advice end up gaining it back, and there are many different reasons for this that are both psychological and physical.
A major and sustained change in perspective and behaviour is needed to lose weight with diet and exercise. Simply telling people to eat less and move more isn't enough.
Telling someone with obesity to just "eat less, move more" is like telling someone with depression to cheer up, or someone with alcoholism to just drink less.
Change needs to be initiated from many angles
Psychological, dietary and lifestyle changes all need to come together to provide a successful result.
Everyone has different drivers and triggers that lead to over eating. Accessing and modifying these ‘programmed’ behaviours are the key sustained success.
Cognitive Behavioural Therapy (CBT) has been proven to assist in making the changes needed to gain a sustained result for life. Willpower will come and go depending on the other demands of life at the time.