A pony crossed the river. It knows from the squirrel that the water is deep, but the old cow tells it that the water is actually shallow. Inspired and encouraged by his mother, Pony decided to go down the river to try the depth of the water himself, and finally found that the water was neither deep nor shallow, so he crossed the river smoothly. Why are there two different answers? The reason is that the squirrel and the old cow answered the pony according to their own experience. Squirrels and old cows are different in size, so naturally they have different views on water depth. Fortunately, the pony is not hearsay, but proves the fact that "the water is neither deep nor shallow, and I can cross the river by myself". It can be seen that only practice can produce true knowledge.