An atheist buys an ancient lamp at an auction, takes it home, and begins to polish it. Suddenly, a genie appears, and says, "I'll grant you three wishes, Master."
The atheist says, "I wish I could believe in you." The genie snaps his fingers, and suddenly the atheist believes in him. The atheist says, "Wow. I wish all atheists would believe this." The genie snaps his fingers again, and suddenly atheists all over the world begin to believe in genies. "What about your third wish?" asks the genie.
"Well," says the atheist, "I wish for a billion dollars." The genie snaps his fingers for a third time, but nothing happens.
"What's wrong?" asks the atheist. The genie shrugs and says,
"Just because you believe in me, doesn't necessarily mean that I really exist."