Why was the prince happy when he was alone and had a human heart?

In reply to the swallow’s question on why he was weeping, the Happy Prince says that “when he was alive and had a human heart, he did not know what tears were.” When the prince was alive, he lived in the Sans-Souci Palace, where sorrow was unknown. He spent his days playing about the palace gardens with his companions and dancing in the big hall. Since the palace was surrounded by a great wall, beyond which he never ventured during his lifetime, the prince lived happily in his beautiful environs and died without knowing the meaning of sadness or sorrow. He was always happy, and that is why he was called the “Happy Prince.” However, upon his death, when his statue was set on a tall column, from where he could see the whole city, the prince was finally able to see all forms of suffering among the city dwellers. He saw sorrow, and that made him cry.
Throughout the rest of the story, the prince then uses the swallow to take away bits of precious metals from parts of himself to give away to needy people in the city. The swallow first takes a big ruby from the sword of the prince, then sapphires from his eyes, and finally the gold that covered his body. All these are given to poor people in the city. The prince and the swallow, together, help to alleviate the suffering of a few people in the city.