Lectures
There were a few things Zayn had to take into consideration when he was being trained by Merlin.
Even before he was taught the Double Saber Kalivan technique, a long time passed in which he was taught many other things that were just as important. Being oblivious to the basics when it came to wielding a weapon came with that disadvantage. Merlin's lectures were thorough but they drained his energy much faster than he expected.
The first thing Merlin focused on was Zayn's physical fitness. It was very important to maintain a good physique when it came to handling weapons effectively. The physical demands of close combat were not to be underestimated. That was the first big hurdle Zayn had to overcome.