A journal is an audit your future self can actually read.

Memory edits quietly and in your favor, smoothing the parts that were sharp and losing the ones that mattered. A line written on the day does not do that. Months later it shows you the real shape of a stretch of your life instead of the summary you have been repeating since, and the two are often surprisingly different.

Three lines a night is enough. What happened, how you felt, what you are unsure about. Read a month of it in one sitting sometime and notice what keeps appearing, because the repetition is the part worth knowing.