Gu Shenwei guessed that the seeds of betrayal were probably planted when Shangguan Fa sliced off one of his Eighth Son's palms.
In the Western Region, there was a one-legged king but not a "one-handed king". After losing his palm, Shangguan Nu was doomed to be unqualified for the highest position in the castle. There seemed to be only two roads ahead of him: die in an internal struggle or find an alternative way out.
History often operated in cycles. Shangguan Fa had cruelly eliminated all of his competitors yet was unable to be equally merciless with his own son. Perhaps, he knew that his Eighth Son's future had hit a dead end, and keeping the latter alive was merely so that his stronger sons would have someone to target.