The evening after Jonas experience a sunburn for the first time, he feels " desperately lonely." Why?

Jonas feels a sense of loneliness because no one else in the community has never known pain. The environment, which is completely controlled, eliminated pain. Jonas feels alone in knowing that he is the only person to feel what real pain is.

They have never known pain, he thought. The realization made him feel desperately lonely, and he rubbed his throbbing leg. He eventually slept. Again and again he dreamed of the anguish and the isolation on the forsaken hill. ”