I have been keeping a sort of journal since 2008 - I was born in 1991. Since then I have written 275 entries which comes out to about 17 entries a year. My journal today is one of the most precious things I own.
You are not special. That means that what you are living through, feeling and thinking - other people will experience too. As a father, I hope that that is going to help me at least be able to better understand my children when they are young adults. At best, my kids will be able to read some of my entries which might help them navigate their own issues.
I have never truly identified with an author. The simple fact that the book is well tells me that that person is different from me - given my poor writing skills. I think that in order for a journal to be truly you have to be able to identify with the author. If the author is your father, grand father or uncle - you have seen their flaws. In my mind that makes it much easier for me to identify with them.