For years, I've always thought that the idea of keeping a diary/private journal was stupid merely because if you are going to write down your private thoughts in a book, you are just asking for someone to eventually read it if they ever get access to it.

But now I realize that it's probably a good idea to write down your thoughts of the day because our perspective of the world is constantly changing and keeping track of that could help you grasp a better understanding of the world. Just like any other journal, it's supposed to track your "improvement", in this case, your perspective of the world.

Also, I don't think it should necessarily remain private forever. Decades from now, you probably wouldn't even care about even your most embarrassing thoughts/moments. Maybe not publicly, but you could probably pass down that diary/journal to your kids and grandkids in your golden years, it would probably help them out too.