When you wake in the morning, your subconscious loads four memories in to your short term memory slots. If its a good day, and youre about to go on holidays, it loads holiday planning thoughts and you are happy. If its a shit day, it loads a 17th iteration thought in slot 1, an argument you had yesterday in slot 2, and leaves the other two empty. It runs those two horrid thoughts on a loop. It has been for days now. You arent aware of it, but those two thoughts are your entire world today. In every spare moment they will be front of mind, festering away, driving you down in to a deep, dark, fearful, angry place in your mind.
The goal is that when you wake in the morning your brain loads long term mission in to slot #1, and short term plans to achieve long term plan in to slot #2. Slot 3 is full of appreciation for how good your have it, slot 4 is thinking about dinner with your friends tonight.
Journaling is how you pull the shit decks out of the slots and replace them with the positive ones. It is a way to reset your mind. By quickly pondering your long term goals, your plan to get there and why you are excited for that to happen, your bring it to front of mind(slot 1). Journaling is one of the Superpowers. It is such a simple thing, and if you dont do it, you might spend days, or years, unnecessarily running shitty tapes in your slots, which you could have so easily swapped out for good ones.
Meditation is obviously the perfect activity to couple with journaling. I try to do them back to back. Personally I write first, meditate second. But it might work best in the opposite order for you.