When a fish swims, he swims on and on, and there is no end to the water. When a
bird flies, he flies on and on, and there is no end to the sky. From the most
ancient times there was never a fish who swam out of the water, not a bird who
flew out of the sky. Yet when the fish needs just a little water, he uses just a
little; and when he needs lots he uses lots. Thus the tips of their heads are
always at the outer edge (of their space). If ever a bird flies beyond that edge
he dies, and so also with the fish. From water the fish makes his life, and from
the, the bird. But this life is made by the and the fish. At the same time, the
bird and the fish are made by life. Thus there are the fish, the water, and
life, and all three create each other.
Yet if there were a bird who first wanted to examine the size of the sky, or a
fish who first wanted to examine the extent of the water and then try to fly or
swim, they will never find their own ways in the sky or water.
-from the Shobogenzo