21 Day fix. Don't understand how it's so successful

I am amazed at him much people are losing on it. These are REAL people I know who like me dont have much to lose. I'm thrilled if I lose a pound a week but I know people who have lost 5 in the first week using it. . I know that it will tail off but I don't understand the science of how this works, compared to me who,is eating the same amount of calories but not using the system. This is a genuine question by the way. I'm not a coach trying to plug the programme. I just can't understand it and want to know if its worth investing.