Manicure ruined by abrasive headlight cleaning?

Question

My friend simply ruined a perfectly good set of headlights trying to remove a slight surface oxidation by wet sanding them. I told her it was not advisable on such expensive lens but she listened to her swollen head boy friend who claimed " the sandpaper can't scratch when its wet". and he said it would be so easy she could do it her self.

Not only did she ruin her manicure but her headlights are white now! Her boy friend is MIA and now she has to replace the lens to pass vehicle inspection.

Why do people keep falling for the " use sandpaper to clean your headlights" line?