A tree planted will not fall by a heavy wind if it is provided with a strong support. Even a tree that sprouts and grows naturally will fall if it does not have strong roots. Likewise, a feeble person will not fall if he has a strong supporter but a healthy person, walking alone, will stumble on a rough road. What is more, everyone in all the worlds in the universe, except Venerables Śāriputra and Kāśyapa, would have fallen into the three evil realms (hell, realm of hungry souls, and that of beasts and birds) if the Buddha had not appeared in this world to preach His Dharma. However, many of them were able to attain Buddhahood due to the strong tie of having embraced the teaching of the Buddha. Furthermore, such evil persons as King Ajātaśatru and Angulmāla, who were destined to fall into the Hell of Incessant Suffering, were able to become Buddhas solely because they had the good luck of encountering a great man, Lord Śākyamuni Buddha.

Therefore, the best way to attain Buddhahood is to have a “good friend” (zen-chishiki).

San Sanzō Kiu no Koto, Concerning the Prayer Services for Rain by Three Tripiṭaka Masters, Writings of Nichiren Shōnin, Doctrine 3, Pages 203-204.