If there's one thing that This Is Us has taught me, it's that families can change in the blink of an eye.
This Is Us Season 4 Episode 18 drove that point home. Kevin's life was shattered by two huge shocks, and he wasn't the only one making life-altering decisions.
And both baby Jack and the Big Three's first birthdays were bittersweet occasions because of how difficult the year before had been.
The fight between Kevin and Randall was as tragic as it was powerful.
Both of them exploded, showering each other with a lifetime of pent-up resentment and rage, and now they've said things they can never take back.
In all likelihood, Kevin didn't really mean that Randall's adoption was the worst thing that ever happened to him, and Randall didn't mean all that nonsense about how Kevin makes it all about him.
But the things they said to each other can never be unsaid, and from the looks of it, now the two won't talk again until Rebecca's condition deteriorates so much that they're forced to come together to say goodbye to her.
It was especially heartbreaking that this blowup came on the heels of Kevin learning that he was about to be a father.
In other circumstances, Kevin probably would have liked to tell Randall what was going on with him.
He and Randall, like most brothers, are sometimes each other's rock even though they also get under each other's skin, and it's a shame that they threw all that away over all of these old resentments that should have been dealt with years ago.
Kevin: I wonder what changed Mom's mind. Did she say anything to you, Randall?
Randall: She probably thought it was just the best investment in her future.
Kate: Question for you. Do you get progressively weirder as you get older?
It's hard to believe that only a few hours before the blowout, Kevin was laughing and teasing Randall.
Yet at the same time, I can't blame him for being angry.
As Beth said, Randall's methods were suspect.
What Randall called doing whatever it took was using guilt to manipulate Rebecca into doing what he thought was best, and though Kevin didn't know the details, his analysis was spot on.
Randall overrode Rebecca's wishes as if he knew better than Rebecca what was right for her.
I'd like to know more about Miguel's reaction to this decision. Early on, he was resentful of Randall trying to take over Rebecca's care, so it was disappointing that he seemed to be okay with it now.
Did he know that Randall pushed Rebecca to participate in the clinical trial? Hopefully, when This Is Us Season 5 begins, we'll get more of Miguel's feelings and reactions to the whole thing.
Beth, too, resigned herself to Randall making an ass out of himself and made a point of not being around when the crap hit the fan.
Randall: Hey Beth, do you think the clinical trial is not a good idea?
Beth: I think your mom made her own decision. I think the tactics you used to get her there are...mmhmm.
She must have realized there was no talking Randall down from this one. Hopefully, she'll have something to say about Randall and Kevin's rift, and so will Dr. Lee.
Meanwhile, Kevin's news -- and his important accomplishment -- got overshadowed by the fight with Randall.
Besides Nicky, no one acknowledged that Kevin had been sober a year. That was sad.
But Kevin will probably lean on Nicky in the coming months as he deals with Madison's pregnancy, and that's good news.
Nicky's attempt to reform himself during the first half of This Is Us Season 4 turned him into one of my favorite characters, and I missed him after he disappeared again.
Kevin: Listen, I got to get into this meeting. But tomorrow is my one-year-sober. My one year sober is also Jack's birthday.
Kevin: I thought you might want to congratulate me.
Nicky: I'll congratulate you tomorrow.
His relationship with Kevin is a lot of fun and equal parts awkward and supportive. So yay for more of that.
Kevin wasn't the only one making a life-changing decision, as Toby and Kate decided to adopt another baby.
I was surprised that they agreed about adoption so soon. It seemed like they were headed toward another huge argument over it when Kate wasn't sure it was a great idea.
But at least that solved the mystery of who the art curator was whose scenes were spliced into the narrative. Her conversations with Zach made it seem as if she had had a one-night stand with a grown-up Jack Damon, only for it to turn out that she was his sister.
Well played, This Is Us.
I'm still not sure what the little girl with the horse had to do with anything, other than that her father was Madison's doctor and he borrowed her words to convince Madison to tell Kevin about her pregnancy.
Maybe that's all it is, but This Is Us doesn't generally bring random people into the story just to be bit players, so there's likely more to the story than that.
The past and future storylines helped reinforce the points about family being fragile and ever-changing.
Rebecca and Jack's grief over having lost Kyle was poignant as they celebrated the Big Three's first birthday as well being a reminder that Randall being adopted contributed significantly to the family dynamic.
Jack. That song is amazing. So amazing that I'm having contractions.Lucy
And on the other end of the space-time continuum, Jack and Lucy naming their baby Hope represented the fact that the Pearsons/Damons were going to go on no matter what.
Your turn, This Is Us fanatics.
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This Is Us airs on NBC on Tuesdays at 9 PM EST/PST. It will return for its fifth season in the fall of 2020.
Jack Ori is a senior staff writer for TV Fanatic. Follow him on Twitter.