Nichiren Daishonin states in “Reply to Nichinyo gozen”:
It is said that the Yellow River becomes clear once in a thousand years. It is said that a sage makes his advent only once in a thousand years. A Buddha is said to be born only once in innumerable kalpas. Even if you encounter the Buddha, it is difficult to encounter the Lotus Sutra. And even if you encounter the Lotus Sutra, it is still more difficult for common mortals like us, who were born in the Latter Day of the Law, to encounter the votary of the Lotus Sutra.