It's all based on what you believe in.

Someone asked us recently, "Is there any limitation to the body's ability to heal?" And we said, "None other than the belief that you hold." And he said, "Then why aren't people growing new limbs?" And we said, "Because no one believes that they can."

Source: Abraham-Hicks Publications; Excerpted from the workshop in San Rafael, CA on Saturday, February 27th, 1999 #329