Obviously (!), I agree with Barca and Bryaxis. It isn't simply a matter of getting a bow and firing it: training, methodology, type of bow, type of arrow, whether the target was armoured or unarmoured, shielded or unshielded, trained or untrained, etc. etc.
The 'volume' method which appears to have been used by the Sasanids required little training and relied on sheer numbers of arrows fired to cause casualties. In contrast, the Huns relied more on superior skill to select and hit individual targets - hence their reputation: a few specialist archers could cause large numbers of casualties amongst unarmoured and untrained troops.