What's the point?
We naturally tend to pay more attention to negative things in our lives than positive things. They usually stay in our heads longer. If you received a good grade but made a mistake that you are not proud of, you may remember your mistake more than your good grade. Similarly, if someone gives you 10 compliments and one criticism about something you did, you may remember the criticism more than the compliments.
This is called cognitive distortion. You can try to reverse this tendency of your brain by taking a few minutes each day to highlight the positive things you experienced during the day.
By doing the quick exercise of thinking of three positive things that happened to you during the day, you'll be more able to see the positive in your day. Remember, journaling is a way to take a moment for yourself. It's not magic, but it's something that will pay off in the long run.