Why does Sakura tried to kill Sasuke? I haven't been fully understanding it, and it's been nagging me for awhile now. Your smart, so why did she tried to kill him?
Well, she had heard from Sai about how much suffering Naruto was apparently going through because of the Promise of a Lifetime, and felt very guilty as a result of this because from her perspective, she was majorly disappointed in herself for failing to realise how much trouble the promise had been causing Naruto all along.
Now obviously, with hindsight, we know that Sai had severely misinterpreted the situation and was giving Sakura a very false impression here, but at the time, Sakura wholly believed Sai’s words, and it affected her greatly:
But what really cut her deep, was Sai saying that even though Sasuke’s actions were causing Naruto to suffer, he thought that Sakura was indirectly causing Naruto just as much pain and suffering because of the burden of the promise:
And as if that wasn’t enough, Sakura would then hear from Shikamaru that the village had already deemed Sasuke a dead man, and were planning his execution because they couldn’t allow his transgressions to taint their relationships with the other hidden villages:
So Sakura thought to herself that seeing as how Sasuke was already as good as dead, she would take it upon herself to do the deed, not just because she loved him and wanted to save him from the darkness:
But also because it was her own way of atoning for the burden that she had apparently placed on Naruto which was causing him so much suffering. Sakura wanted to carry out Sasuke’s execution by her own hands, and she was fully prepared to face Naruto’s resentment as a result, because she thought that was what she deserved:
So yeah, that’s how Sakura came to the decision to kill Sasuke - She rationalised that because he had already been marked for death, she may as well do it herself, because she wanted to save the target she loved from a life of further misery, and wanted to atone for the suffering she caused her friend.