Before the weight is lost they go back to their old habits. They make progress for two or three weeks and start to soften on their effort thinking "well I'm progressing quickly enough but it doesn't matter if I cheat a little and progress a bit slower this week, but I'll still eat clean enough to make progress, just not quite so much. I deserve a bit of a rest" and then after that week the old habits return and the tiny bit of progress they made is instantly undone. No willpower.