Why is the youth compared, metaphorically, to a 'jaded horse'? Why is this description appropriate?

Into the youth's eyes there came a look that one can see in the orbs of a jaded horse. His neck was quivering with nervous weakness and the muscles of his arms felt numb and bloodless. His hands, too, seemed large and awkward as if he was wearing invisible mittens. And there was a great uncertainty about his knee joints.

The youth is unbelieving....... it's as if he's been tricked into participation. He's in shock; horses trust their masters........... to be jaded would men that trust has been broken. This doesn't mean it was intentional, but everything now becomes real and he's not only reacting mentally but physically as well.