Anne feels that no one understands her. 

Anne is so tired of fighting with everyone and listening to their criticisms that she decides it is better for her to talk to herself instead of to any of the other Annex occupants during meals. 

First, they're glad they don't have to listen to my continuous chatter, and second, I don't have to get annoyed by their opinions. I don't think my opinions are stupid but other people do, so it's better to keep them to myself. (Tuesday, August 10, 1943) 

Anne is a boisterous girl with a big personality.  In school she was assigned to write an essay titled "An Incorrigible Chatterbox” and she did well, but her teacher got tired of how much she still talked and then assigned “'Quack, Quack, Quack,' said Mistress Chatterback.'”  The class found this amusing. 

Anne’s reputation as a chatterbox does not end at school.  The members of the Annex often complain that she talks too much or about nonsense.  This is why she comes up with the idea to not talk to anyone.  However, while she wraps it in justification, Anne is actually very lonely.

Sometimes I'm so deeply buried under self-reproaches that I long for a word of comfort to help me dig myself out again. If only I had someone who took my feelings seriously. Alas, I haven't yet found that person, so the search must go on. (Tuesday, June 13, 1944) 

Anne’s world has grown very small since she went into hiding.  There are very few people to talk to, and most of them are adults.  The only person close to her age is Peter, and they can’t decide if they want to argue or fall in love.  Anne feels frustrated, confused, and misunderstood.  The fact that she is in hiding just compounds and exaggerates problems that might already be there.