How does one become possessed by a demon?

Voodoo Doll, 4th century : photo credit: Marie-Lan Nguyen via Wikimedia Commons

“There are two equal and opposite errors into which our race can fall about the devils. One is to disbelieve in their existence. The other is to believe, and to feel an excessive and unhealthy interest in them. They themselves are equally pleased by both errors and hail a materialist or a magician with the same delight.” C.S. Lewis

In the New Testament, Jesus drove countless demons out of men and even children and g...