Conundrum

He had everything, Billy. Anything he wanted, he could have immedietly. If he wanted food, it appeared. Friends, they would also appear. But Billy could never leave his castle. He had never even ventured outside for more than a few minutes.
One day, he was walking down a corridor when he saw something he had never seen before; a girl, running about his castle, that he had not created!
"Who are you?" He asked.
"I'm Jenna" She said. "and I'm here to get you out"
"Get me out? I like it here, I have everything."
"Ah, but there is one thing you can't have here. Come, follow me" she said mysteriously.
Following the girl, Billy reached the roof of his castle, a place he had never been before. It was night, and a huge full moon shone down on them with its etheric gaze.
"I've never seen this before. How did you know about it?"he asked.
"I've stared at that moon all my life, from the streets below. We don't have much down there, but it feels like we have everything on a night like this"
Billy was confused. How could one have everything when they had... less than everything? It made no sense.
As they walked, they went through more narrow corridors and steep outer ledges, until it happened.
Jenna slipped and fell, hanging from a platform just out of Billy's reach.
"Wait! please hold on. Why did you come here?"
"To show you what you can never have." she said, before letting go.
It made sense to Billy, all of a sudden. He realised what he could never have. After sitting there for a while, he made up his mind and jumped.
He could never have happiness.