Yes, popping/scratching a pimple causes permanent scar. Even without manipulation some individuals with genetic predisposition or severe forms of acne will develop scars but more so if you pop them. Chicken pox also leaves behind a similar type of scar. Scars happen when acne or a chicken pox lesion involves deeper part of your skin called dermis, where collagen and elastin are destroyed. When the skin heals, the collagen formation is not complete. Thats why you get a scar.