To understand why this trope resonates, one must consider Japanese domestic architecture and social norms. Traditional and even many modern Japanese homes have thin walls, sliding doors (fusuma) that don't lock, and a cultural emphasis on shared space. Privacy—especially for male adolescents—is often limited.
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The protagonist is alone. Mother is out shopping. The door is locked (or so he thinks). He puts on headphones. The outside world ceases to exist. This is the "shikotteru tokoro" – the private ritual. The art usually depicts a mundane room, sunlight streaming in, an open laptop. Normalcy is the killer. Kaa-chan no Tomodachi ni Shikotteru Tokoro Mira...