Dong Zhou wrote:Sima Yi vetoed one reform he admitted was a great idea simply becuase Cao Shuang's proposed it.
Talk about holding a grudge haha
When I was reading up on Wang Ling yesterday, I realized that Sima Yi left a bloody mess wherever he went those last couple of years. I'd love a more trustworthy source on Wang Ling but, depending on what I read, he can potentially come off as sympathetic which makes Sima Yi eradicating his family sound more brutal. Then there are other sources where he was a flaming butthole to Man Chong and was basically asking for it. Either way, Sima Yi still comes off as rather brutal in nature to me, he absolutely did not put up with rebels which in hindsight is ironic.
It's hard to get a read on Sima Yi's intentions because his window of opportunity after making his move was fairly narrow, he made his move on Cao Shuang in 249 and got ill and died right after subduing Wang Ling in the fall of 251. So he had time to get in there and make his changes, but not really enough to stomp his feet and boldly claim that he was doing away with Wei. Considering how Cao Pi and Cao Rui demonstrated a decent amount of faith in him, I find it difficult to clearly justify his actions from 249 on, grudge against Cao Shuang or not. I do try to be sympathetic to him in general, but as mentioned he clearly left his sons with the ability to overthrow Wei if they felt inclined to do so, intentional or not. Occam's Razor would, I'd guess, suggest that he knew what he was doing and intended it.
Line of succession: Yes, the moment you show some weakness in selecting the expected candidate as your successor, you open Pandora's Box. Happened with Yuan Shao, Liu Biao, and Sun Quan right in that very era, and there's also Liu Bei's case. Cao Fang probably came off as competent enough to Cao Rui, perhaps showed promise and intellect as a youth, and was the obvious candidate to choose according to tradition. Selecting a young heir was never ideal but was never definitively
negative, some child emperors in China later grew up to be great rulers.
It's also worth pointing out, I wouldn't exactly label it a bloodline
since there were so many cases of adoptions, but the direct family line, father to child succession, was paramount. DragonAtma's Zhuge Qiao is a great example to demonstrate this, they basically tried to do whatever they could to maintain that succession somehow. So Cao Rui passing over the young Cao Fang to pick another relative without any strong justification wouldn't pass muster.