In the scar of Xuanyuan sword, why is the heart of Jianchi missing a corner?

The sword pool is a part of Tuo Yuwen, which is the part where Tuo Yuwen banishes evil thoughts. Is kind, so his heart is missing that part of evil thoughts, it is not a complete Tuo Yuwen, but only in this way can he bring Xiaoxue out, but later, after many obstacles, Tuo Yuwen changed back, and the memory of Jianchi will always be in his heart. Go and have a look.