Holding the stone, Jon went ahead and made his world-changing wish: "I wish ..." Jon hesitated. How could he possibly know the repercussions of a wish meant to effect the whole world? Then it occurred to him. A wish that couldn't possibly go wrong.
"I wish that the world was a better place." He finished.
Unfortunately, what hadn't occurred to Jon was that 'better' is quite a relative turn. There was no way of knowing how the stone would interpret it.