Isolation makes Anne more conscious of her own inner thoughts and conflicts. A headstrong teenage girl to begin with, she feels more alienated than ever, especially in regards to her tense relationship with her mother. She uses her diary to express the feelings she cannot share with anyone else in the annex. The circumstances of their hiding make Anne turn to her writing as a way of sorting out her thoughts and impressions. Her introspective nature becomes sharper in the annex overall, and as a result, Anne becomes more perceptive about her situation, her identity, and her dreams for the future.

Isolation's impact on the other annex inhabitants creates conflict among them. Everyone becomes irritable and they begin to argue amongst themselves. Mrs. Frank and Mrs. Van Daan fight. Mr. Dussel constantly criticizes Anne. The Van Daan adults are shocked by the liberal parenting style of the Franks, feeling they are too lenient with both Anne and her sister Margot. Margot becomes jealous of Anne once she and Peter become confidants.

Another negative effect isolation has on the annex party is an increased tendency towards self-interest. Mr. Dussel never extends much sympathy or aid towards his fellow annex-dwellers. Mrs. Van Daan is stingy with her own material goods. Such behavior causes more resentment among everyone in the attic.

In spite of this, some relationships are allowed to develop in a positive way due to this proximity, such as the budding romance between Anne and Peter. The two initially dislike one another, with Anne believing Peter is cold and boring, but the two grow closer over time. Anne realizes there is more depth to Peter than she believed and this increases her empathy.