Diets are bad if all you do is reduce your food without counting nutrition. It might work at first but you could bounce back. You are true in that scenario. But people who calorie deficit and workout to add to their diet, most of the time will succeed. I've seen it myself, my grandmother was overweight and even as an elderly person, she could fix her diet and started working out. You know what happened? She became slimmer, her face was more obviously beautiful, so much more happy and less moody. Your physical state can reflect some of your mental state. If my grandmother can loose weight from a diet I'm sure others can.