(1) Everyone in the story expects him do die, or otherwise be a failure, and GRRM has a sense of irony;
(2) He is the last of the Arryns, a noble and ancient house that has lasted thousands of years;
(3) He loves the ancient stories, and knows them all by heart;
(4) He is a wicked aim with a bowl of porridge or a chamberpot;
(5) Even at aged 6, he knows a "bad man" when he sees one. Tyrion fans hate him for this, but it is the simple truth.
(6) He has a healthy fear of Littlefinger; smart kid.
(7) Ever since his mother's death, he won't let anyone come near him with a blade; smart kid.
(8) Even while terrified, he managed to be brave while coming down the mountain: "The winged knight was brave and so am I. I am an Arryn." The "high saddle" path defeated Cate coming up; but on the more-difficult task of coming down, Sweetrobin calls it "nothing" and exhibits only a mild shaking.
(9) Stronger than he looks. (He can hurt you flailing; you would not think it, but he can).
Edited by Fearsome Fred, 15 May 2012 - 06:46 PM.