It's because of the ego, the soul, or something like that.
Each person's ego is different, just like no two leaves are alike.
This leads to some people being compatible with [Fire Magic], some being compatible with [Thunder Magic]. Some people having high compatibility with [Fire Magic], some have low compatibility with [Fire Magic]. Even with equal compatibility, it won't be the same, just like how a certain amount of water can be stuffed into all kinds of cups of all kinds of shapes.
Of course, that alone was not enough for Kain to conclude, after all the human body had the same nature that no two bodies were exactly alike. But Kain had a different way of thinking.
Previously, Kain had asked teacher Alisa why she chose this teaching method, she said that she didn't know clearly, it was just that it had been passed down from many generations of Magus.
