This is related to the Buddhist notion of the "opportunity of human form". (In the Fukazazengi, Dōgen renders this as 人身の機要, read "ninshin no kiyō".)

To be born a god is too easy -- it's hard to turn to the dharma when life is so good. To be born a demon or an animal is too difficult -- it's hard to practice the way when life is so tough. As a human, we recognize fairly early that life does not always go our way; but we are not without some control and capacity for disciplined practice. It's this combination that allows us to (a) want to practice and (b) be able to practice.