In an answer to this question (Why aren't phaser rifles used more often?), one author quote from Major Kira:
It's Federation standard issue. A little less powerful, but with more options; sixteen beam settings, fully autonomous recharge, multiple target acquisition, gyrostablized, the works.
If it has multiple target-acquisition, then theoretically you should never miss. I can see hand-phasers missing (unless they also have target acquisition) but why would a phaser-rifle miss? Bad targetting computers? Or are the phaser beams really slow and you can literally dodge them?