I used to start and never finish diaries.  After a certain number of weeks, months, or years of non-entries, I'd find the diary in a drawer or fallen behind the books of my bookshelf and uncomfortably read through what I'd written. 

 "Ugh. why did I devote so much time to that subject. It didn't turn out to be important.  I'll start a new diary and talk about actually important and relevant things that reflect who I am and life in general and this time the diary won't have Chad Michael Murray and Hillary Duff taped on the cover but it will be  _______ (Insert: [abstract and artsy] [dark and chic] [leather and sophisticated]

...and legit for my current tastes"

Sometimes I edited or commented on previous thoughts and noted the new date. I remember reading through my age 8 journal at age 10.  On one page, I drew an arrow and circled some original comments and wrote, "Valerie Wilder, age 10, year 1998, says that is stupid" Two years later I looked back again, crossed out both, and wrote, "Valerie now age 12 says who cares"

Take away points for the story:

1) Valerie did/does/probably always will analyze even the inane
2) Don't discard diaries (wave your heart-throb clippings in the air and smile. Whip them out at the dinner party) But 
3) Don't be afraid to change your mind (that is, unless you find yourself spinning in crossing-out circles. You do have to remain sane) Because
4) Although continuous and spread over time, the you you are now matters more than the you you were then but not as much as the you you will be, and does not detract from the you you always is, and that, dear future self, is fortune-cookie-quality wisdom.