Diario del búnker

Using diary format makes the story so intimate and raw, but I wonder if that was planned from the start or evolved during writing. How does this choice affect the pacing and tension?

The book kept me on edge, especially with the way hope flickered then shattered. Am I the only one who felt emotionally drained by that constant tension?

The confined space and intense focus on mental states make it stand out, but I'm curious whether the author drew from real psychological experiments or personal experiences.