The Karmapa gave another example illustrating how important and necessary all traditions of Buddhism are. Imagine, he said, a large copper vat filled with milk. It takes four people to lift up, using their strength equally so that the milk does not spill out. There may be some little difference between the four people but basically they are the same. Nevertheless, the Karmapa explained, if one of the four could not carry their side, the milk would spill out. And it would go out even faster if one of the four thought they could do the lifting on their own. So the four need to cooperate in the project of lifting the vessel, which the Karmapa explained as an analogy for the Buddha’s teachings being carried by different traditions. If one side tried to carry the entire vat and spilled the milk, the whole of Buddhism would be diminished; if even one of the other schools disappear, it means that Buddhism is disappearing, so everyone needs to work together. In sum, he said that if the teachings, which are the antidote for our afflictions, become the cause for afflictions to increase, we are finished, so we should consider this carefully.
~Karmapa: Cultivating the Delight of Rejoicing and the Freedom from Prejudice