The following is the exerpt from "Dharma Talk: The Four Immeasurable Minds By Thich Nhat Hanh".
"The second aspect of true love is karuna, the intention and capacity to relieve and transform suffering and lighten sorrows. Karuna is usually translated as “compassion,” but that is not exactly correct. “Compassion” is composed of com (“together with”) and passion (“to suffer”). But we do not need to suffer to remove suffering from another person. Doctors, for instance, can relieve their patients’ suffering without experiencing the same disease in themselves. If we suffer too much, we may be crushed and unable to help. Still, until we find a better word, let us use “compassion” to translate karuna.
When I was a novice, I could not understand why, if the world is filled with suffering, the Buddha has such a beautiful smile. Why isn’t he disturbed by all the suffering? Later I discovered that the Buddha had enough understanding, calmness, and strength. That is why the suffering does not overwhelm him. He is able to smile to suffering because he knows how to take care of it and to help transform it. We need to be aware of the suffering, but retain our clarity, calmness, and strength so we can help transform the situation. The ocean of tears cannot drown us if karuna is there. That is why the Buddha’s smile is possible."
I feel that enough understanding, calmness and strength the Buddha had mean enlightenment. Buddha must have been able to transform all sufferings instantly without fail.