The more you grind, the less you depend on luck, since you're bound to get what you're aiming for eventually.
Just because someone got an item when killing 5 monsters and you got it after killing 500, doesn't mean he will get it every 5 monsters, nor that you will get it every 500, when you both kill thousands of them, it should even out. It's just about working and luck will eventually start to show up, or better yet, it won't be that big of a factor anymore.