If only! lol
Actually, it was said by Descartes (and philosophers always make things more difficult!).....
The meaning is something like: If someone is wondering whether or not they exist, that (the thinking) is itself proof that they do exist (because there is least an "I" that is doing the thinking).
EDIT: "Meow", are you saying you believe that dumb people don't exist? 'Cause, I see dumb people every day..... They definitely exist!