He seemed quite talented in picking up Xiaoyao martial arts, to the point where TSTL praised him early on after teaching him a lightness skill: “Unexpectedly you learn it with just one round of guidance, granny’s divine eyes did not misjudge your talent." Admittedly she later insulted him as stupid, but still; Xu Zhu was said to have a 'first rate' memory, even if his comprehension was weak.
So why was it that he was so horrible at Shaolin martial arts? Was it simply because he honestly didn't care about martial arts? Bad teachers? What was it?