Then the word easy is being used in two senses. Technically losing weight is extremely easy. It's a closed problem. It might be not-easy in a way that varies

Then the word easy is being used in two senses. Technically losing weight is extremely easy. It's a closed problem. It might be not-easy in a way that varies from individual to individual but to say that it's not-easy should be qualified in some sense to show that it's a psychological/will power/whatever problem and not because we have an incomplete understanding of nutrition.