Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
First Person (Limited): Anne Frank
The story is told through Anne Frank’s eyes, and is told with Anne’s voice. We are completely situated within Anne’s viewpoint throughout the book—it was, after all, her honest-to-goodness diary. It's incredibly intimate.
What this means is that we only see the characters and the events that take place through the lens of Anne... even as Anne herself is filled with a confusing maelstrom of hormones, adolescent mood swings, paralyzing fear, and intense claustrophobia. Anne herself even points out that she often writes when she is most angry, frustrated, or depressed as a way to relieve those feelings. (She also occasionally writes when she is feeling most happy and invigorated.)
Because of that, we see Anne’s world through her strongest moods, which probably don't reflect her typical daily experience. We need to understand that what we are seeing through her diary is life as she experienced it on certain occasions—the occasions that prompt her to pour her heart out.