Part of growing up is realizing almost everything your mom said was wrong. This is especially true when it comes to the human body (how many of you grew up with the "masturbation will make hair grow on your palms" thing?) where, as you'll see, mom often failed to do her research.
"If you shave, your facial hair will grow back thicker!"
Fellas, do you remember when you first started getting those wispy specks of hair on your chin? They were patchy and thin, but dammit you loved them, and you knew that it was merely a matter of months before you looked like those guys from ZZ Top. Do you remember what your mom told you? "If you shave your beard/moustache/muttonchops off it will grow back thicker and look much nicer." So you continued shaving it until, sure enough, five years later you had a perfectly serviceable moustache.
Actually, the only reason you ever managed to grow those whiskers was simply time. Renowned (read: gets the most tail) dermatologist Dr. Jerri Hoskyn M.D., says here that, "Shaving is just a method of cutting the hair at the skin surface and has no effect on the part of the hair ... where growth and pigmentation occur." Who's to argue with a man who had to go through eight years of medical school to cure pimples?
So why do moms perpetuate this one? Most likely out of the embarrassment most mothers of pubescent boys feel. It seems you didn't have the good fortune to hit the ground running with puberty like we Cracked staffers did, and it took you a few years to start looking and sounding like Powers Boothe. Consequently you had a fuzzy neck beard, and your parents didn't want to be seen in public with you until you shaved it.
So instead of telling you straight up that you were a repulsive pock-marked abomination and having to hear you whine in your broken girly voice, they simply lied and told you shearing hair makes it stronger and thicker, knowing you would do it--and keep doing it--in a futile attempt look like Grizzly Adams.