I once knew a guy who was that good. I used to take all of my glass cutting work to him and I always hung around to watch while he did the work for me, but even with tips that he freely gave me, I still couldn't do it very well.
He told me that people would frequently want to buy the glass cutter that he was using, because they were convinced that it was a special one. He would tell them that it was the same as the ones on the shelf, but they still wanted the one that he was using. He would then sell them his old used cutter and then take a new one out of the box and begin using it. He said that it wasn't the cutter, but the technique that made the cuts accurate, and after watching him for a while he convinced me. But I still can't cut glass well, not even straight lines, even after all his tips and help so many years ago.
Central North Carolina