The opening sequence ends with Pamela Kim dying from her disease with Margot tearfully playing a song next to her in her final moments. This leads to the fracture in David and Margot's relationship which kickstarts the whole plot.
After spending some time searching through his daughter's social media sites, David eventually comes to the realization that he never really knew his daughter at all. It's also something that many parent viewers could really relate to.
David's heartbreaking reaction after he learns of Margot's apparent murder. Sure, it turns out to be a lie later, but at that moment, David thought that he had really lost his daughter for real and that everything he had done to find her was All for Nothing. It all ends with David permanently deleting the video recording of the young Margot celebrating his birthday and calling him "Best Dad Ever", clearly feeling depressed that he couldn't live up to it.
