The most telling moment in the first season of This Is Us is easy to miss.

Rebecca Pearson (Mandy Moore), having just learned that she and her husband are about to have triplets, goes to lunch with her mother to ask for help. The walk-up starter apartment the couple has just rented — after assuming she was pregnant with only one baby — will be far too small for three kids. She needs money, or somewhere to live, or something like that.

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At the restaurant, Rebecca’s mother orders her daughter a Diet Coke, putting emphasis on the “Diet.” It’s a character moment, meant to illustrate how Rebecca lives in the shadow of an overbearing parent who micromanages everything about her life. It’s the kind of small character detail the show often nails.

There’s just one issue: Diet Coke didn't exist until 1982, and the scene takes place in 1980. In and of itself, this isn’t a problem. The series’ writers take great pains to make their 1980s scenes feel of a piece with their 2017 scenes — the better to emphasize the universal nature of the human condition. At worst, they didn’t know Diet Coke wasn’t around in 1980. At best, they figured somebody hearing the name of Diet Coke’s predecessor, Tab, would be pulled out of an emotional scene by brief period piece nostalgia.

But I call this moment “telling” for a reason: This Is Us’s greatest flaws almost all stem from getting small details wrong in favor of maximizing the emotional weight of the storytelling. And over the course of the series’ flawed first season, those small details have added up to something that threatens to topple the show.

This Is Us is most interested in big moments — to its detriment

This Is Us isn’t just the biggest new hit of the 2016-’17 TV season. It’s also the biggest surprise hit. Broadcast networks are supposed to be done for when it came to breakout dramas, yet This Is Us airs on NBC, one of the original big three networks. And family dramas are supposed to be the shows that die on the vine while cop dramas, medical dramas, and legal dramas thrive.

But This Is Us routinely tops 10 million viewers per episode — and often surpasses 15 million viewers per episode once DVR viewing is factored in (to say nothing of its streaming viewership, many forms of which are barely counted by Nielsen). The reasons for its success are complicated — and include everything from a smart promotional campaign to the national mood being uniquely receptive to a comfort food drama like this one. Late last year, I delved a bit more into how the show became such a hit. But why this show? Especially in an age when other breakout dramas tend to be the Game of Thrones and American Horror Stories of the world?

Well, if you break down This Is Us into its component parts, it has far more in common with Game of Thrones or American Horror Story than you might expect. Yes, where those shows emphasize big, shocking moments — plot twists or bursts of gore or surprise deaths — This Is Us emphasizes moments of tenderness and comfort. But it still trades in moment-based storytelling, complete with the model’s inherent flaws.

Briefly defined, moment-based storytelling is a form of TV writing that emphasizes a scene-to-scene model over the episode-to-episode model favored throughout TV history. It often doesn’t matter if any given scene contradicts any other given scene if both scenes are as intense as possible. A lot of the time, the goal is less to tell a coherent story and more to prompt discussion.

Moment-based storytelling can be brilliant. I’ve loved several seasons of American Horror Story (mostly the even-numbered ones, for some reason), and Game of Thrones is frequently masterful. But the form paradoxically has its eye on the big picture — the grand sweep of the entire series — alongside the smallest possible unit of on-screen time, the scene, without much regard for everything in between. And it’s what’s in between that has defined TV as a medium since its inception.

This Is Us has more respect for the episode than other moment-based shows. Each installment has a unifying theme or idea, and it has produced at least one standout, standalone hour that has little to do with the overarching storylines (“Memphis,” the first season’s 16th episode, which is among the best TV episodes of 2017 so far).

But the story This Is Us tells is still epic in its sweep. It aims to tell the story of the Pearson family, from the moment in 1980 when Rebecca and her husband Jack (Milo Ventimiglia) go to the hospital so she can give birth to triplets, all the way up through the present. It’s been filling in those 36-and-a-half years piecemeal, letting us know little bits and pieces (Jack is dead! Rebecca is remarried!) here and there. It’s even set a few short scenes in the distant past, when the family’s progenitor first immigrates to America.

Series creator Dan Fogelman is clearly interested in generational change and the ways families evolve over time. But the result is that individual episodes or storylines are largely swept away by the show’s bigger picture, of filling in all those details, and every storyline must focus, as much as possible, on the immediate, moment-based pleasures of whatever’s happening. In the case of a family melodrama like This Is Us, that means feeling stuff. Nothing is ever painted with any nuance. Sad scenes are SAD. Happy scenes are HAPPY. And so on.

And that explains both why This Is Us sometimes works so well — and why it so often falls on its face.

The devil is always in the show’s often bizarre details

While talking about This Is Us with Vox contributor Kelsey McKinney (who recaps the show for Refinery29), she pointed out to me that the second you step back from almost any storyline, it ceases to make sense. On a scene-to-scene basis, the emotional tug works well enough. But when you try to examine the characters as actual human beings, their actions don’t conform to any recognizable reality. Details trip you up if you think about them too much.

This is most evident in how the show struggles to balance the stories of the grown Pearson siblings — Kate and Kevin, two of the three triplets Rebecca carried (the third died at birth), and Randall, a black son born the same day as Kate and Kevin, whom Rebecca and her husband adopted. (Here I will state that the show’s cast is generally excellent, across the board, and carries much of the show’s weaker material.)

Randall (Sterling K. Brown) is now a grown man, trying to reconcile his racial identity with his upbringing in white suburbia, having met his biological father, William (Ron Cephas Jones), who is dying. This story is delicate, beautifully told, and mostly without moments that make you catcall the show for its most ridiculous impulses.

Randall’s journey is obviously deeply researched by Fogelman and his writers, who clearly spoke to and read about transracial adoptees, looking into how they can feel adrift in their own lives, terrified of making mistakes lest everyone they know reject them.

Kate (Chrissy Metz) and Kevin (Justin Hartley) are not nearly as lucky when it comes to the show’s storytelling. Kate’s storyline focuses almost entirely on the fact that she’s overweight. Her fiancé, Toby (Chris Sullivan), frequently treats her in objectively awful fashion, but the show doesn’t dare question him, because he loves Kate, and that’s supposed to be enough.

A frequent complaint leveled against the show — every Kate storyline is about how she needs to lose weight — makes more sense when viewed through the lens of the moment-based storytelling model. Of course the series would keep hammering that point; it’s what’s viewers most recognize about the character.

Kevin, meanwhile, is worried he’s too pretty, and nobody takes him seriously as an actor because his big break was on a sitcom. That’s pretty much it — and the show’s slow, scrambling realization that his storyline lags so far behind Randall and Kate’s has been hilarious to watch unfold. (It culminates in him receiving a call from Ron Howard, which only brought to mind a very different family show: Arrested Development.)

Kevin’s story is also the foremost example of how This Is Us’s focus on big, emotional moments — dramatic monologues and heartfelt conversations and sweeping gestures — obscures good storytelling. On its surface, the story of Kevin’s Broadway debut is deeply poignant, especially when he ditches opening night to care for Randall during the latter’s dark night of the soul.

But if you think about it for two seconds, everything goes to shit. Would Kevin really abandon his play on such a pivotal night? And why would he make that choice at the last possible moment, right before he’s supposed to go on stage? And then how would he somehow manage to sweep that debacle under the rug, for the most part?

The little stuff starts to add up, and suddenly you’re rolling your eyes. (Don’t even get me started on the midseason love triangle Kate briefly finds herself stranded in.)

This Is Us is serious in its mission to provide viewers with TV comfort food, but it seems to misunderstand that the best TV comfort food is still built around more or less realistic human beings.

To use a very similar show as a comparison point, the characters on Gilmore Girls still made coherent emotional sense as people. The show itself might disappear into its elaborate comic set pieces, but it never pushed too far in one direction or another when it came to the very real pain that its three generations of characters felt about their relationships (or lack thereof).

This Is Us can write a great scene or monologue, but it still struggles to craft realistic character arcs, often because it’s hiding big story turns behind its back.

Much of Kevin’s behavior in romantic relationships, for example, turns out to be motivated by a marriage that dissolved 12 years before the series began. The act of hiding this detail from the audience meant that Kevin often seemed like a blithe jerk who was intended to be charming. Once viewers knew his history, it didn’t cause the character to snap into place. In fact, he made even less sense.

The show presents people who are struggling with deeply rooted emotional traumas, but acts as if said traumas can be resolved with feel-good, network TV moments.

Great TV requires nuance. That’s where This Is Us struggles most.

To a degree, much of what bedevils This Is Us might have to do with airing on broadcast TV. For far too long, most of the characters would have long conversations with each other in which they essentially recapped their storylines for each other, in case the audience hadn’t yet caught up. (This was particularly true for the three Pearson siblings.)

And the shame is that when it wants to be, This Is Us is a very smart show on a visual level. “Memphis,” in particular, lets visuals and music carry much of its story about Randall and his biological father William taking a trip to the titular city so that William can make amends before he dies. The characters still probably speak more than they strictly need to, but the stripped-down storytelling suits the show well.

Yet elsewhere, This Is Us seems terrified that viewers might conclude the wrong thing about a scene, or not understand its emotional subtext. Its fondness for plot twists often obscures what’s really happening, to the peril of everything else. And the show’s desire to withhold the details of the central tragedy of the Pearson family’s life — the death of the kids’ father — has yielded lots of clumsy scenes where characters have to talk around what happened. It’s the dawn of the season one finale, and we still don’t know what happened, which only raises expectations in the audience’s mind that the ultimate “answer,” which is purported to come in said finale, will be something huge. (It seems more likely it will “just” be a drunk-driving accident.)

The fear that the audience won’t understand something is typical of broadcast TV, but This Is Us is such a big hit that it could probably buck the trend. (Generally, shows that perform well in the ratings are granted some degree of creative freedom.) Instead, it’s leaned ever further into that lack of nuance.

Of course, it’s possible the series is going somewhere with this. It spent most of its first season presenting Jack as a perfect father and perfect man, whose death utterly devastated all who knew him.

And in the flashbacks to the ’80s, he really does seem pretty perfect — until the last handful of episodes, when some of his darker sides come out. What if, for instance, he was a great dad, but not always the best husband, and his tragic death has stopped his loved ones from remembering his less impressive moments? That could be interesting.

Fogelman is a smart writer whose credits include, among other things, the screenplay for the movie Crazy Stupid Love, the winning alien sitcom The Neighbors, and the “first woman in baseball” drama Pitch (which also debuted last fall and probably won’t be back, even though it was much better than this show). He has to know that if This Is Us is going to continue for years to come, he has to deepen it beyond these initial early impressions. And episodes like “Memphis” give me hope he can pull that off.

But every other storyline on This Is Us suggests all involved are satisfied with the show as it is, or still under pressure from the network to over-explain what’s happening. And if that’s the case, the series might fall victim to the perpetual nemesis of the moment-based show: Once the audience knows how Jack died — and thus the show’s full picture — there’s less reason to keep tuning in. Puzzle pieces are only interesting in and of themselves as you’re trying to assemble something larger. Once the full picture is in place, how much more time do you want to spend looking at it?

This Is Us airs Tuesdays on NBC at 9 pm Eastern.