The problem with being too focused on something was that you missed things happening around you. While she did indeed succeed with the first throw after his 'challenge', her focus blinded her to the seemingly idle and meaningless gesture he made during her second throw. The breeze that answered his movement disrupted the dart's flight at a critical point, thus causing it to land beyond its intended target.

He made a small noise of mock dismay at the sight. "It would appear that you have failed."