It's not a coincidence. "Journal" and "Journey" are derived from the same word root - "jour". It's French for the word "day".
And that makes sense, since both of them are a record of days of sorts.
A journal is a written record of the day.
A journey is the experience of where one travels in a day, or week, or month, or years.
Each day unique, even if there are routines involved. Each experience worthy of reflection, of thought, and of remembrance.
Writing things down, capturing them in words, is a way of preserving the roads traveled. It helps gain insight into things like personal development as well as a reminder of occurrences, of emotions, of milestones.
"What did you do today?"
Best done without an eraser? I think so. There is a sense of the rawness of the moment, of memories without varnish; get it down, get it out, and then - if need be - post reflections on the reflection. Insights after the fact. Would have, could have, should have - reports without regrets.
Deliberate. Unembellished. Constant.