(CNN)The following contains spoilers about the first season of "This Is Us."
Fox executives fielded questions in January about how the season's breakthrough hit, "This Is Us," wound up at NBC. They suggested the show -- produced by sister unit 20th Century Fox Television -- was a better fit there, citing a legacy of family dramas that included "Parenthood" and "Friday Night Lights."
In truth, though, "This Is Us" has eclipsed those series in terms of its popularity. And the search for explanations about why the program caught on has proven elusive, despite plenty of analysis, including a Wall Street Journal story that sought to answer "Why 'This Is Us' Makes Us Cry."
Certainly, the cleverly conceived pilot -- which operated in two different time periods, one involving a young couple (Milo Ventimiglia, Mandy Moore), and the other devoted to their three grown children -- planted a strong hook. Yet even then, there was reason for skepticism about where the show went from there once that cat was out of the bag.
So why has "This Is Us" -- hardly the first drama to utilize a time-hopping narrative -- popped? The reasons seem as complicated as the show's structure, but have a lot to do with consistently strong writing and performances, two of the show's major subplots and its introduction of an enticing mystery.
Perhaps foremost, the relationship between the overweight daughter Kate, played as an adult by Chrissy Metz, and her very funny suitor Toby (Chris Sullivan) has been simultaneously sweet and heartbreaking. In a world filled with plus-sized people, primetime TV rarely dares depict them in romantic settings, along with the insecurities and hardships Kate has faced, both in her younger and grown-up incarnations.
The bonds forged between Randall (Sterling K. Brown), who the central couple adopted as a baby, and his biological father (Ron Cephas Jones) proved equally compelling, and took on a deeper emotional resonance when it was learned the dad was terminally ill. That built toward a send-off filled with pain and regrets, but ultimately a sense of fulfillment -- that the two finally connected, if only briefly, while there was still time.
Finally, "This Is Us" has benefited from the guessing game built around the death of Ventimiglia's Jack, raising questions about how and when he died, as well as how his wife wound up with Jack's best friend (Jon Huertas). Not surprisingly, that storyline's trail of breadcrumbs has been sprinkled out sparingly, but just liberally enough to keep the audience invested.
NBC has already extended the program a major vote of confidence, renewing it in January for two more seasons. That sets up a challenge for the writing staff, to be sure, but also provides a sense of security -- both for them and the audience -- and time to gradually flesh out existing threads as well as conjure new ones.
Identifying the alchemy that goes into creating a successful series is often tricky, a guessing game played with the benefit of hindsight. Moreover, a show like this one -- which relies heavily on its warm, melancholy atmosphere -- can easily alienate viewers with one or two serious missteps.
For now, though, "This Is Us" has more than earned its three-hankie reputation, and having firmly established its characters, looks destined to wind up crying all the way to the bank.
The "This Is Us" season finale airs March 14 at 9 p.m. on NBC.