Tally’s retort makes it clear that she believes pretties are happy solely because they look like everyone else—in other words, she believes that unhappiness stems from difference, and that difference is an intrinsic part of being a teenager. Conspicuously, she doesn’t express any possibility that the uglies are unhappy simply because they’re teenagers and are still developing. Importantly, unhappiness not something that would normally be cured with plastic surgery, so this implies that there’s more to the surgery than just changing one’s appearance.