The number one reason he states is because people tend to take shortcuts. This manifests itself in many ways. The most obvious one is in fad dieting. You know the type: I'm going to my high school reunion and need to lose 150 pounds by next Friday! So, if I drink nothing but slim fast 3 times a day for the next 10 days, I will be skinny.
No you won't. YO'll be sick to your stomach, probably have diarrhea from all the liquid fiber, and after a few hours you'll be so hungry you'll eat whatever is within your reach. End result: you'll be fatter than ever at the reunion.
Situation number two is the deprivation diet. These are the diets that eliminate an entire food category or dietary necessity, like protein or fat. God constructed our bodies in such a way that in order for us to live and survive we need basics like carbs, proteins, and fats on a daily basis. Yes, eliminating a group over time will definitely result in weight loss, but it's not good weight. It's probably muscle wasting weight and the first time you go off a diet like this you will gain back real weight immediately because your poor body has been deprived and robbed of a nutrient for so long.
Skipping meals is another way people think they can lose weight, and for some reason skipping breakfast is the favored meal to eliminate. DUMB! Your body needs fuel to make it run, just like a car needs gas ( or in some cases, like the Prius, electricity!) If you don't gas up the car it won't run. If you don't fuel your body it will go into survival mode which means it won't metabolize anything you've got in your body stores and you will shut down in order to save your life ( metaphorically speaking!)
Bulimia is another shortcut and just as stupid and dangerous as full out anorexia. I was bulimic for over 30 years ( good GOD, I'm old!) and I have always thought that getting rid of food before your body naturally eliminated it, sounded like a good idea. Isn't it funny how we can trick ourselves into thinking something so stupid and bad for you is really good for you??!! The real problem with bulimia is that after a while your metabolism never knows what is going to happen next so it just basically shuts down and your are forced to externally get rid of the food you've eaten because your body doesn't know what to do and basically stores everything that goes into you.
Shortcuts. They may work to get you someplace faster when your drive. They don't work when you diet.