"In the context of learning, intrinsic motivation is motivation that stems not from external factors like grades and status, but rather from genuine interest and ambition. Like altruism, it assumes no reward. But – like altruism – it is difficult to corroborate. Even if Sally, your best student, completes the Extra Credit assignment out of pure enjoyment, it doesn’t mean she isn’t expecting external rewards like approval and attention."
Via Beth Dichter