You'd be surprised how hardy the human body is. Torso has a lot of vital organs that would be lethal depending on what they punctured, depth, if they pull the blade out, the blade being serrated or wide, ect., but most importantly, response time for wound care and surgery. If your character has medical knowledge, they could reasonably get away with it. If not, it does take a while for someone to bleed out. With that in mind, it's possible they found help within that window thus surviving it.
I'd simply refuse that information to the reader about how they managed to survive a knife wound. They don't really need to know anyway. It won't break the immersion. It'll come off to them as suspense, "Oh, shit! Is he/she really dead?!" Write it in because it's critical for the story to work. That's just my two sense. It's your story, do as you please. 😊
