I'll also add that you can't undo a bad diet over x years in much less time.

Obese people are shocked that changing the course and loosing fat takes time. Of course, they didn't also get obese in a year.

When you're getting fatter and fatter you don't even register couple extra kilograms, compared to if you have a healthy habit of measuring weight/lean body mass/body fat weekly (this is crucial, because measuring JUST weight is just half-assing yourself) and staying in shape. One who's doing that will notice the weight change even without measuring, your more attune to your body and you "know". It's ironic that more better you're in shape, easier it is to stay in good shape, but hey that's how law of fittest works.