That is because it is fluid and it can wear the rock away. That which moves trumps that which is stagnant. In tropical climates, one avoids standing water, for therein lies the beginnings of disease and death. It is only that which moves and is free that provides life. We must make certain that our education is fluid and flowing and unconstricted.
Movement is energy.
Energy is life. When energy is contained, it builds up and ultimately explodes. When we contain their energy, we create an explosive potential in them. Or, perhaps just as sadly, we kill their spirit and their will to be active, creative people. And that may be a greater violence.