This Is Us is a show based in reality – it's not a time travel series, it's not a fantasy show. It's a show about people like you and me, living their lives. Except the twist is their lives are presented all jumbled up, like a bunch of unorganized photographs in a shoebox. How does one give timelines straight in a series that is not based on fantasy? Turns out the showrunner wrestled with how to make that work for the series. The answer was Jack's facial hair on This Is Us works as a visual time stamp.
Jack's facial hair is a bit of a joke among fans because it's always changing.
- In the late 1970s, right around the time the Pearson children are born, he sports a full beard, shaggy hair, the hippie look.
- The end of that decade sees Jack shave all that hair off. He cuts back the hair and goes into what is his "pornstache" mode. It's his "square family man" look.
- The mid-1990s see Jack go a little grungy. The beard comes back, but it's not a full faceful of hair. It's the look of the era, the goatee.
These are the three main time periods the show has done so far over the first two seasons.
Fans are vaguely aware that the show will be going back in time even further this season, perhaps providing a new look: Clean-shaven Jack.
For most of the This Is Us audience, bouncing around from era to era, at least without some serious plot markers. This Is Us' entire deal in the first episode is that the time periods aren't distinguishable at first glance, because they want the audience not to realize this is really the story of one family.
That meant, even after the pilot, the show couldn't start adding in markers either. There's no "1981" caption at the bottom of the screen every time the show shifts back to right after the trio are born. There's no "1989" every time the action moves to the kids being around 9 years old (or in Season 2, "1990".)
In fact, the show doesn't really want you to know what day or year it is, because they don't want Jack's death, which occurs when the triplets are teenagers, to be revealed too quickly. Part of the mystery of the first two seasons was that viewers didn't know when exactly Jack died. It was about putting together the clues of what year and month it is when Rebecca throws him out for drinking, when in the school year it is for the kids, etc.
Now on some level, the kids are markers. There are the children who play the triplets (Parker Bates, Mackenzie Hancsicsak, and Lonnie Chavis) and the teenage actors for the 1990s (Logan Shroyer, Hannah Zeile, and Niles Fitch.) But for scenes where the kids aren't involved, especially as the show goes further back in time to explore Jack and Rebecca's early years, Jack's facial hair is the best guide fans can have.