What is the most important lesson in life?

A man sees a snake dying in flames and decides to free it from the fire. As soon as he catches it, the snake bites him causing excruciating pain. The man immediately drops the snake and the reptile falls back into the burning flames.
At this point the man, looking around, finds a metal pole and uses it to take the snake from the flames again, saving his life.
Another man, who had seen what happen, approaches the man and asks him: "This snake bit you! Why are you trying to save his life?"
The man replies: "The snake's nature is to bite, but that won't change my nature, which is to help."
Don't change your nature just because someone has hurt you. Don't lose your goodness of mind, but learn to act carefully.