Among all the symbolism contained in the series, alert viewers pinpointed the significance of the number seven. In an early scene, Luke shows Nell his self-protection ritual of tapping stones and counting to seven, saying, "It has to be seven... that keeps you safe. Sometimes you gotta do it a lot. Like, a lot a lot." The twins' beds just so happen to be seven steps apart from one another, and there are also seven members of the Crain family... until things go south, of course.
The loss of Olivia turns the Crain family into a gathering of six, after which their lives remain in ruins. After Nell's death, Shirley points out the number issue again when she says, "There were seven of us, and now there's five, because two of us decided to die." However, the final shot of the series shows the four remaining Crain children gathered alongside their spouses — of which there are three, as Luke is still single — and since they once again form a group of seven, they're the perfect group to stay safe by his childhood standards.
