Even with its ever-expanding mythology, Supernatural‘s monster of the week episodes remain at the core of the series.

Supernatural‘s tenth season has put Dean at the center of the show’s mytharc, as the elder Winchester began the season as a demon. However, even when he was cured, the Mark of Cain remained and has continued to affect him. Despite this heavy mythology, the last several episodes have been monster-of-the-week format. Some might even call them filler and grow impatient as they wait for movement in the season-long arc.

But we’d remind these fans to remember that episodes like “There’s No Place Like Home,” “About a Boy,” and “Halt & Catch Fire” come from a long-standing tradition.

Since its first season, Supernatural has had a specific structure for its seasons: We open each season by picking up the pieces from the previous season finale and setting up the new season-long arc. The second (and sometimes third) episode usually builds on the themes of the season premiere. We then move into a stretch of standalone episodes until the mid-season finale, which moves the plot along and ends with a cliffhanger.

The mid-season premiere then picks up those pieces and sets up the back half of the season. After that, we move into another stretch of monster of the week episodes that mix in with the occasional mytharc-related episode until the penultimate episode of the season, which sets up the season finale. The season finale usually resolves some issues and set up others via cliffhanger for the following season.

Rinse, wash, repeat.

There’s usually very little variation from this structure. It’s comfortable. Fans generally expect this type of structure from the veteran drama.

But for all that comes from the big plot-heavy episodes that regularly deal with end of the world-type stakes, the monster of the week episodes are equally important. Seriously. These episodes propel the season forward, though in a different way from their mytharc counterparts. In doing their duty of “filling space” between the plot-heavy episodes, they are tasked with exploring the emotional fallout of the events of plot-filled episodes.

While there is no denying the varying quality of the monster of the week episodes from the last ten years (bugs and racists trucks, anyone?), the successful ones have something very important thing in common: They reflect the emotional journey of the Winchesters.

And the best of the best monster of the week episodes do so subtly. They offer a slightly off-kilter mirror to Sam and Dean’s issues that forces the brothers to face their demons, both literal and figurative. These episodes keep the heart of the series, the human response to the fantastical, beating.

The most recent episode, “Halt & Catch Fire,” is an example of a successful off-kilter mirror in that there were no direct parallels between the brothers and the characters they came across on the hunt. However, the guilt eating at Delilah for her part in a fatal hit and run provided Dean an opportunity to reflect on his own feelings regarding the Mark of Cain. They may not have been the healthiest of feelings, but no one has accused the Winchesters of being well-adjusted.

Meanwhile, the grief of the young widow who held on to a spiritual echo of her husband reflects Sam’s inability to let his brother go. Her convincing her husband’s spirit to let go and move on presented Sam one option for reacting to Dean declaring he didn’t want to keep looking for a cure at the end of the episode — to let him go — though it’s far more likely he won’t do so.

We would argue that no matter how you felt about the case, the emotional core of this episode was solid. And that is what made it a successful monster of the week episode. It kept the Winchesters’ story going — their emotional story — despite not focusing on the season’s mythology. And it did so without hitting viewers over the head with painfully obvious parallels.

Next week it looks like we’ll have another plot-centric episode, but that episode wouldn’t have its inevitable impact without the work of the monster of the week episodes, the unsung heroes of Supernatural.

Supernatural airs Tuesdays at 9:00 p.m. ET on The CW.

What are your favorite ‘Supernatural’ monster of the week episodes?