So THIS Is Why Kevin & Randall Are Fighting In That 'This Is Us' Flash Forward

Spoilers ahead for This Is Us Season 4, Episode 16. It's becoming abundantly clear on This Is Us why Kevin and Randall are fighting in the flash forward to their 40th birthday. It's going to be a slow burn towards them not speaking at all, and the argument is not really because of one thing. It's more like they're just diametrically opposed in every way.

Justin Hartley, who plays Kevin, confirmed as much to Entertainment Tonight. "It's more than a misunderstanding," he said of the impending fight. "I think it's a philosophy. It's like, 'This is how you handle your life and this is how you deal with things and this is what you think. I go about my business a different way,' and they just can't [see eye to eye]."

That became clear when dealing with what Rebecca's treatment should be for her memory issues. Randall wanted his mother to participate in a nine-month clinical trial. She said she wanted to enjoy what time she had left, and she didn't want to spend that time in a faraway state for nine months without her family and husband. Rebecca is still perfectly capable of making her own medical decisions, and her children should respect this one.

She's always been a strong woman, which the flashbacks in Tuesday's episode showed. She wasn't afraid to call her husband out for not trusting her sense of direction in New York, and years later she also declined to go out with Kevin's acting teacher after he made fun of the horse and carriage rides in Central Park. She wasn't going to let him ruin such a sweet memory of her husband and it was a good reminder that she's always been headstrong. Whether it was pursuing Jack despite her family's qualms about him, going back to singing later in her marriage, or reaching out to Randall's birth father behind his back — Rebecca lives her life by her own rules.

She's trying to do that again with this clinical trial, too, and while Kevin is happy to let their mom make her own choices, Randall is convinced that they know what's better for her. It's a shame that these two points of view might ultimately mean that they'll miss out on spending some quality with their mom, as a family, just like in that 40th birthday flash forward.

Kevin and Randall's differences don't just stem from their response to Rebecca's illness. They also both see Jack's death in very different lights. Randall told his brother that he blames himself for not stopping his dad from going back into the house fire to save the family dog. He thinks every day about how life would be different if Jack hadn't gone back in and had survived. Kevin said he never thought about that and that he believes that no one could have saved their father that night. Kevin doesn't dwell on things, and never has. Meanwhile, Randall can be obsessive with how much he overthinks things. They really have this very core separation in how they approach life, and it's being exacerbated by the Rebecca situation.

Sterling K. Brown, who plays Randall, told Entertainment Weekly that the fight between Kevin and Randall rates at about a six or a seven, with Jack and his brother Nicky's years-long estrangement being a 10. At least that means we can hope for an eventual reconnection, if it's not as bad as Jack and Nicky's argument. Brown also encouraged fans to stick it out through this tough time, because he thinks that this family will always come back together. "This family never forsakes: They show up for each other, and you find a way to move forward together," Brown said. "That’s something that most families can relate to and will find hope in, that you come together. Even when you fracture — and you may fracture for a period of time — you ultimately, at the end of the day, come back together."

Kevin and Randall just need to find a way to come back together before they waste what little time they have left with their mom.