1. You can do anything
It doesn't have to be written out like you see in movies. A journal can be on video, kept in a scrapbook or even drawn out! Journals (or diaries, if you prefer) can be whatever you want them to be. Starting a journal can be a lot of fun, and that means it can be whatever you feel like creating to capture your favorite memories. You can keep it a secret, or show it to anyone. How you journal is completely up to you.
2. It's your personal time machine
Who says looking back at memories isn't time travel? You go back in time by just seeing a picture from when you were in middle school, or a goofy video you shot last week with friends. Sometimes you even stumble across something you may have forgotten about. Everything you put down in whatever your journal is gives you a chance to take a step back in time.
3. It's a friend who always listens
Everything can be put down in words, and it doesn't matter if it looks like a mess. You can rant all you want, get every inch of all your feelings out without being interrupted. It's just you and your thoughts. (But it's always good to talk to a real person.) You'll eventually come back to it in the future, and maybe find out that you learned something from that one bad day.
4. You always learn something new
Sometimes lessons appear out of nowhere, and sometimes they're captured in your journal. You learn more about yourself in the quiet moments when you're working on your journal. Your younger self said something amazing, but at that time, it didn't seem like it. Or you can see how far you've come since then.
5. It's tough, but worth it
It really is hard to keep something like this up every day, but that's the thing. You don't have to do it every day! It can be a day where the most amazing thing happened, a day where you just have a lot on your mind or even the days where it seems like nothing happened but you still want to add it. Make it yours, and it will be easier. It really is worth it -- the end results can be amazing.