So i was doing a holster today and the curvature of it was a pain in the a** to sew i couldn't see one side. So i figured i would try the two needles in one hole simultaneously trick. I've seen it done but it always felt awkward to me, i do one needle then the other. well it works well for finding your holes and helped a bunch however I still pierced the thread a couple of times right at the eye of the opposing needle and my thumb a couple times lol. But that's how a guy learns, leather work is always a new problem and a new solution with new techniques learned as we go.