GnomeWorks said:
In sports, people go into what they call "the zone". Its a moment where the player's ability is at peak (and even sometimes beyond). It involves proper conditioning, training, ability, talent, luck, and mindset. Not everyone can focus themselves like that for every play, indeed it would be to mentally and physically taxing to try. But when the proper amount of psyche, adrenaline, and ability kicks in, the person can perform almost supernatural stunts.
(There are reports of people doing this under extreme duress, like normal average guys lifting a car up on two wheels to rescue a trapped child. when they couldn't normally lift a their own body weight under normal conditions).
So a martial daily has to involve some element of physical action (knocking two arrows) but also some "psyche" to make the trick work. In essence, the daily action occurs because the character feels he's desperate enough to try that maneuver and the player feels the situation warrants his expenditure of his 1/day power. (AKA, situations of extreme difficulty, or to head off a otherwise difficult situation).
So a ranger can knock two arrows and fire them all he wants. In target practice, he might even get reliable at his trick shot. Against a rampaging orc, his ability to clear his thoughts and focus on two arrows is severely limited (due to dodging blows, screaming allies, magical incantations chanted, etc), until he throws caution to the wind, clears his thoughts, closes his eyes, breathes deeply, knocks two arrows, and with one fluid motions aims and fires the arrows in perfect sync. For that moment, he's "in the zone" and he can do miracles.
Will he hit? that's what the d20 is for. Perhaps he does hit and breathes deeply. He's sure he can't do that trick again, it took too much out of him. If it didn't, he's not wasting time on pretty trick shots anymore.
Does this explanation get a bit thin if you realize he can pull off the same supernatural stunt day after day, at least once? Kinda. No more so than the explanation that a first level mage can keep one spell in his brain, but a 5th level one can keep seven (three of which much more complex than his one spell at 1st). Gamism enters the equation somewhere, you can't avoid it.
However, I think the best way to explain it it go with a "in the zone" theory: the PC can try his daily (in theory) all he wants, but that "one" time he needs it to work, it really works (even a reliable one, he wasn't properly in the zone before it succeeded) it works. After that, he's kinda "blown" his focus for the day and no matter how he tries, he's not getting that same level out of his game again until he's rested, ate, and got a couple hours to recharge.
How's that?