Precision is one, if not the most important thing with the bow... but if he had to say, what mattered most when firing an arrow, was the mental state of the user. Emotion can play a very big role in using this weapon, like any weapon, really, but with the bow, it matters a lot more than a sword.
After all, with the blade, you can just swing it around even if your stress levels are through the roof, with a bow, being stressed can be the difference between hitting your target and missing completely.
It's why he always took a deep breath before firing the arrow, to try and calm himself down so he could hit the exact place he wanted, though, for him, being calm wasn't the problem; it was his skill; he wasn't very precise, ironic since he used a rapier. But it just went to show..
