It was common knowledge that no one could go into a dungeon if there was already someone inside. That was a rule that no one could break. But Jason knew that any rule could be broken. He tried to enter the dungeon anyway and he realized that he really couldn't go inside even when he used all of his strength to hit the barrier protecting the entrance.
That was when Jason decided that he was just going to destroy everything. If the dungeon wouldn't allow anyone to enter as long as someone else is inside, then he would get rid of the dungeon itself Something that doesn't exist can't prevent him from going inside it.
