Huh... I'm surprised there hasn't been a King Eric thread until now.
Poor King Eric... There seem to be a number of YAFGC readers who are quite sure that the man doesn't have two spare brain cells to rub together.
I, for my part, have become convinced that he's quite clever (within the limitations imposed by the medium). While Goblins aren't known to be the sharpest knives in the drawer, Eric fooled them into thinking that they'd fooled him (I think, unless I was fooled), thus preventing them from attacking him when he foolishly went out to investigate possible foul play in the dead of night.
Hmm... On second thought, maybe he's not as smart as all that...
But he has excellent night vision, and that makes up for a lot.