It often doesn't work in the sense that people try to achieve a calorie deficit by eating less, which causes their appetite to increase significantly. Many people are unable to resist overeating in our industrialized societies that constantly bombard us with addictive foods. So yes, a calorie deficit is necessary, but it's also necessary to have a way to deal with appetite or else maintaining a calorie deficit becomes unsustainable.

That's why plant-centric diets are a great choice - you can eat as much as you want to satiety, and still be able to lose weight.