The biggest problem in weight loss (beside the fact that you shouldn't do any dieting as this should be a lifestyle change), is how to maintain the weight once you reach the healthy goal.
I'm having a hard time figuring out how to keep the healthy weight and the best way for me is to exercise in addition to a strict cal limit. Exercise will increase your burning rate, and you have to figure how to balance it with your eating habits because you won't know how your body is burning while at rest for a while. This is the main issue, it is harder to maintain this fight than to lose weight on a simple low-cal limit.
I met a lot of folks who successfully lost weight but gained it back and lost it again, it took them 3-4 times in a row to figure out how to maintain their healthy weight. I'm already in my second battle against this. I found the best method is 16/8 fasting method, eat 8 hours and 16 hours fasting and I already am losing far more weight than anything else. This is so much easy to maintain even when I'm reaching my goal.
It's kind of like people winning the lottery and most of them just bankrupt themselves in a year. There's no real good educational program in US that teaches both kids and adult how to focus on what you eat and how to maintain the weight.