Dogen instructed,
It is said in the secular world that a castle falls when people start
to whisper words within its walls. It is also said that when there
are two opinions in a house, not even a pin can be bought; when there
is no conflict of opinions, even gold can be purchased.
Even in the secular world, it is said that unity of mind is necessary
for the sake of maintaining a household or protecting a castle. If unity
is lacking, the house or the castle will eventually fall. Much more,
should monks who have left home to study under a single teacher be harmonious
like the mixture of water and milk. There is also the precept of the
six ways of harmony1. Do not set up individual rooms, nor practice the
Way separately either physically or mentally. [Our life in this monastery
is] like crossing the ocean on a single ship. We should have unity of
mind, conduct ourselves in the same way, give advice to each other to
reform each other’s faults, follow the good points of others, and practice
the Way singlemindedly. This is the Way people have been practicing since
the time of the Buddha.