The focus on Syd's father is more profound in the novel. His suicide is the ghost haunting every page. Her grief, confusion, and anger about it are the engine of the story. The series mentions it and uses it as backstory, but the daily weight of it isn't as palpable. In the journal, you feel her trying to understand him, blame him, and miss him all at once. The adaptation had to spread its focus across more characters and subplots, so this central, devastating pillar of her life becomes just one of several plot points.