Nichiren Daishonin states in “Reply to Hyo’e-sakan (Hyo’e sakan dono-gohenji)”:
Changes certainly occur when the high tide yields to low tide, when the moon rises and sets, when summer gives way to autumn, or winter turns to spring. The same is true when a common mortal attains Buddhahood. At a critical moment, he definitely will encounter the three obstacles and four devils. The wise will rejoice, while the foolish will retreat.