We had a guy come to the gym about 6 months ago. He had an argument with his previous trainer and was looking for a new place. Anyway, he has finished in the top 4 in national amateur tournaments so we were glad to get him. I was working mitts with him and I threw a slow left jab just to see how he'd handle it, he parried it with his left hand. I couldn't believe it, so I did it again and threw a right behind it, of course he parried the left jab again with his left hand and the right would have hit him easily if I didn't pull it. I asked him if he always did that and he said that nobody had showed him the obvious problem with parrying the jab with the left hand. He has mostly corrected that now, but bad habits are hard to break. His previous trainer was a nationally ranked amateur in the 60s so it wasn't like he didn't know anything about boxing. The guy we had was in tremendous condition and was extremely intense so he had done well without learning some basic boxing.