Ok.
Some people delude themselves utterly when it comes to portion control, and don't have the self control not to clear everything from their plate..
They will 'guess' at how much a table spoon of grated cheese is, and end up chucking a handful of the stuff on their plate - but really, a table spoon of grated cheese is only a pinch - 10 grams.
But once it's there, they eat it.
It is very very difficult to convince them that it's just as wasted as fat on their arse than as food in the bin.
The only way around this is to give them some digital scales, and tell them to calorie count and weigh everything - hence weight watchers working.
It is a psychological or behavioral thing, it's not as simple as "Stop putting things in your mouth" - because they then don't know how much they are allowed to put in, and will feel guilty for every bite - and will be hungry - and will hit the vending machine hard.
People who are very overweight did not get that way because they were too lazy not to - I have been a size 20, it's not nice, it's not fun, and I absolutely hated being "The big girl" - I wanted to be a p[retty little princess. It's no use having "Nice hair and a lovely personality" if nobody wants to stroke your hair or talk to you!
It's because they just don't know where to start. They are thinking "Eeek got to lose 3 stone, eeeek I can't do it, sod it, I'll go to Evans."
And (full on autorant in progress) it really does not help that shops are pandering to everyone's wish to be 2 sizes smaller by cutting their clothes 2 sizes bigger. It allows the illusion of - Oh, I must be the same weight as 5 years ago - I'm the same size.
Newsflash - you're not. YOu could be 2 stone heavier.