"I will not let him die..."Ser Jorah gave a bitter laugh. "Khaleesi or queen, that command is beyond your power." (65 Daenerys 8.44-45)
A Game of Thrones is also very interested the limits of power. Here Jorah points out that all human power is useless in the face of death. Now here's something to think about: if they can't really win against the natural forces of the world, how do you think they'll do when they're fighting against the coming winter? Uh oh.