He's not a tame lion

CS Lewis, an Ulsterman, is one of my heroes. His Aslan chronicles, now on film, are great children's stories.
Talking of Aslan, Lucy asked
. Then he isn’t safe?’
‘Safe?’ said Mr. Beaver; ‘don’t you hear what Mrs. Beaver tells you? Who said anything about safe? ‘Course he isn’t safe. But he’s good. He’s the King I tell you’”–
Why. We're told in 'the last battle"
“He is not a tame lion,” said Tirian. “How should we know what he would do?'
He can't be boxed in!