As someone who has been fat and not-fat throughout my life, I think literally everyone knows that it is simple to lose weight by eating fewer calories. That does not mean it is easy. If you are already fat, which can happen almost without you noticing by eating 200-300 calories too much a day over a year say, or as a result of some brain malfunction (both have happened to me), then eating the calorie deficit require to lose weight is mentally very hard to to.
As a thought experiment, imagine what you eat per day. Now halve it. Would you be having a good time?
As a thought experiment, imagine what you eat per day. Now halve it. Would you be having a good time?