One diet works for all? No, that is absurd.
Humans are as different as they are similar. Sure, we share most of our genetic code, but the subtle differences in genes are what makes us each unique. These subtle differences result in different body types, eye color, hair color, height, and, yes, metabolism. Metabolism is a physiologic dance that occurs in our bodies that determines how much and fast we burn calories. We have adapted to our environment to survive and certain metabolic advantage that allowed the people that we are to today to survive the nature as it was back then. I will explain more, but unfortunately, these metabolic adaptations also make it so that we both more likely to be overweight and less likely to respond to one single diet.
The relationship between our genes and our environments makes us each unique and thus results in differences in how adapted to certain foods and diets. Our genetic differences have resulted from environmental pressures that have given the advantage to one trait or another. For example, descendants of humans that lived in hot, arid climates often have an enhanced ability to handle hot temperatures and thus retain water and salt more and thus avoid dehydration. In cold environments, humans developed an ability to build more metabolically active brown fat to keep them warm in winter months. The first example is an advantage in desert environments but may hinder good health in an individual who has a high salt diet but lives in a cold environment, and excess fat clear is a disadvantage in warm climates.
We, therefore, need to know our personality and bodies type to understand what sort of lifestyle would maximize our opportunity to have a healthy weight. If you know the foods that hinder your ability to stick to a single serving, you can keep them out of your home and office. If you know that you like meat and do not like grains or beans, a vegetarian diet would be very difficult to maintain a healthy macronutrient profile. The fact is that there is not a single diet that all of us can maintain or lose weight. What works for one person will not work for another, so it is exceptionally important for us to individualize our diets. This being said, you cannot live on cheesecake alone.
The bottom line: Individualizing the type of diet you eat is important for weight loss and maintenance. No diet is ideal for all. Each person is different, and without personalizing the diet, you will be unlikely to maintain it.