If you want to stay in shape and get healthy, there are two major things you have to consider your diet and your exercise. Yes, many people believe that these two things don't always work, and they would be correct, but no matter what method you choose you need to consider these two factors as an integral part of that program. It's possible to have a perfectly healthy diet and a terrible level of physical fitness and visa versa. This does not make for a good way to go, regardless of how you plan to lose weight. You need to consider the long term bodily consequences of your actions and develop a health plan for diet and exercise that you can sustain permanently.
Many people get into these horrible "garbage in and garbage out" diet methods which just don't work. You are what you eat, as the saying goes, and if you're eating poorly you will look and feel poorly. You need to eat well, even simple and tasty things made naturally can make all the difference in your health. It's true you can lose weight with just dieting alone, as many diets such as using green coffee or the HCG protocol prove all the time. However, it's important to commit to some long term changes, once you reach your weight loss goals. Changes that can carry you through for years to come and maintain the weight you've lost. You need to provide your body with the tools it requires to build muscle (which burns fat and increases your metabolism).
Combining Both To Achieve Real Results

The best results a person experiences are going to be from combining both diet and exercise. Sure, the HCG diet, for example, doesn't allow for exercise during phase 2. However, it's encouraged for users to do this during the maintenance phase and beyond. Your exercise method will help you to burn off calories and build muscle, which is essential to maintaining a high level of metabolic rate.
Going from point A to point B when losing weight is not the best way to do it. You have to think about your body as if it's a living and breathing machine (because it is). A pound of muscle is smaller than a pound of fat (more dense). If you are gaining muscle, you may not be losing weight at the same speed as your fat stores deplete. Just losing pounds is not necessarily a good thing in all cases, and getting discouraged if you aren't losing weight as fast as you want may not actually mean anything tangible about your health. If you are building muscle instead, you're going to be way better off.
Challenges You Will Face and How to Overcome Them
Many people get frustrated quickly when dieting, thinking that if the scale isn't going down they're failing. Nothing could be further from the truth, and you are in fact just letting the scale control you. If you're losing inches, if you're energy is going up, and if you are getting more toned, you're doing the right thing. The scale may not always reflect this. Ask yourself, would you rather be 20 pounds thinner and have no energy or muscle or 15 pounds thinner and have the most energy you've ever had in your life? The choice should be simple, creating muscle always trumps just raw weight loss.
If you are incorporating regular exercises into your weight loss method you're going to burn off calories a lot faster than otherwise. If you have a "cheat day", which people fear more than anything when dieting, it won't really impact you much as you will just burn it off from the exercise. This is not a big deal and isn't something you will even notice in your waistline or on the scale. If you are just dieting this may not be true.
You need to think of diet and exercise like yin and yang, both are essential for your health. You cannot do one without the other and expect an easy road, but both together will bring you to a place that you can actually sustain yourself, have a good amount of energy and also achieve real long term success.