You've probably never seen an adult suck their thumb, but that's only because the vast majority of adult thumb-suckers avoid doing it in public.
Adult thumb suckers are not big babies, Harvey says. Not only did thumb sucking cause dental deformities, but it also caused masturbation.
When I say "adult thumb-sucker," what's the image that comes to mind? The only evidence of my secret is the small callous on my left thumb.
So that leads me to two conclusions: Either adults are afraid to admit to they are thumb suckers, or I'm one of the only people who does it.