There's something irresistibly intriguing about a diary.  It might contain a totally bland description of a humdrum day, BUT there's a chance that within those pages lies an extraordinary insight, strange confession, or shocking secret about the writer.  Do you read it and intrude on someone's private life and thoughts without their permission?  

Absolutely!  Why deprive yourself of the many books that are written as a series of documents, letters, journal or diary entries?  These types of books, called epistolary novels (from the Latin "epistola", or letter) are ways to experience the thrill of reading someone's diary or private letters, without the guilt or risk of being caught.  The movie "Daddy Long Legs" with Fred Astaire and Leslie Caron was adapted for the screen from the epistolary novel of the same name.  Some others you might enjoy are:

 photo courtesy of photosan0