Rant mode on. Losing weight quickly is generally a very bad idea. I meet so many people who have crazy (in my opinion) weight loss goals. Some of the goals are simply impossible to achieve.
The problem with losing weight quickly is that it requires superhuman efforts. Someone making attempts at losing weight quickly would have to put in some extreme dieting techniques and exercise plans. These extreme plans simply are not something you can maintain long-term. Most times losing weight quickly means losing muscle and not just fat.
Please understand that it is possible to lose weight quickly when it is done under medical supervision. A doctor can prescribe a very low calorie diet, but that can cause medical issues which is why you want to do so only under a doctor's supervision.
Honestly, the best way to lose weight is to do so slowly. Losing weight quickly causes far too many problems. In the end people losing weight quickly wind up with sagging skin and a poor body image. They are unhappy when overweight and unhappy when in shape. This is why I recommend doing it the slow way. It takes longer but also lasts longer. Rand mode off.