Every This Is Us (series writing: Kay Oyegun, 27 episodes) fan has been waiting, like, an eternity to find out how Jack Pearson died. It seems like he might have been caught in the fire that burned down the Pearson home, but audiences still don't know for sure. What we do know is that Kate blames herself for Jack's death, even if it still hasn't been revealed why that is. But a subtle This Is Us clue from the midseason premiere hints that Kate actually might not be at fault for her father's death at all.
It's a quick, blink-and-you'll-miss-it moment, but in the complex puzzle that is the circumstances surrounding Jack's death, it's an important piece. In one of the opening scenes of the episode, Kate and Toby are packing up to get ready to visit Kevin, who has been participating in court-ordered rehab ever since his disastrous DUI at the end of the fall finale. During their conversation about the events, Kate says to Toby, full of guilt, "I let Kevin get sent to rehab." Toby, ever the realest, shoots back "Technically the judge at his DUI hearing let him get sent to rehab."
This interaction may seem quick and insignificant, but it reveals a key insight into Kate's character and thought processes. Even though it is obviously not Kate's fault that Kevin developed a serious addiction and ended up in rehab, she is quick to place the blame for the unfortunate development in her brother's life on herself. Later in the episode she once again assigns herself blame, telling Kevin in therapy "I'm sorry too, for taking my eye off the ball. That's you. You're the ball." Even though the sentiment is sweet, and siblings should look out for one another, Kate's apology shows that she tends to blame herself for the mistakes or failures of those close to her, even if in reality, it has nothing to do with her or there was little she could have done to stop it.
So how does this apply to Jack's death? Well, fans should remember that Kate said it was her fault that Jack died, in an emotional confession to Toby. Since then we haven't heard much more from her about it, but that small detail was enough to send fans running wild with theories, from the possibility that Kate started the house fire, to the idea that Jack ran back into the burning house to save Kate's dog, and died in the process. But the winter premiere reveals that most likely, Kate is just blaming herself for something that totally wasn't her fault, like Kevin's entry into rehab.
Chrissy Metz, who plays Kate, echoes this sentiment in an interview with Entertainment Weekly:
"I believe that she really does think it’s her fault, and she does feel responsible for [Jack's death]. No, of course, it’s not her fault, but she has been holding that in forever, and she really does believe that it is."
It would make sense that Kate would feel in some way responsible for her dad's death, especially since the two of them seem to have a particularly strong bond. But, as Metz emphasizes, even if Kate feels that whatever happened was her fault, it most likely isn't. After all, no one else in her family has ever hinted at the fact that Kate might have had something to do with Jack's demise. Considering how intense the Pearson group therapy session got at the end of the Season 2 winter premiere, it's significant Kate's possible responsibility for Jack's death was never brought up.
So while the details of Jack's death have yet to be revealed, it seems increasingly likely that Kate's feeling of guilt is not actually based in any real responsibility. It's just Kate's nature to feel as though she should have been able to fix anything going wrong in her loved one's lives — even when that would have been impossible.