Journaling covers several distinct practices that share a notebook and little else. What separates them is the constraint each imposes, and the constraint is what determines whether the habit survives.
Free writing constrains time, not content
The oldest structured form fixes a duration or a page count and requires continuous writing with no editing, no rereading and no requirement that anything be coherent.
The constraint on time removes the question of what to write about, which is the point at which most attempts stall.
Because the output is not intended to be read, the practice tolerates repetition and triviality, and those turn out to be most of what gets written.
Prompted journals constrain content instead
A prompted format supplies the question and leaves the length open, which is the opposite trade and suits people who freeze at a blank page.
Prompts vary from the specific to the very general, and the specific ones sustain longer, because a broad question produces the same answer repeatedly.
The weakness is fatigue. A fixed set of prompts becomes routine within weeks, which is why published formats rotate or escalate them.
Logging is a different activity altogether
Recording what happened, without reflection, is closer to record-keeping than to writing, and it serves a different purpose.
Its value is retrospective. A log is uninteresting on the day it is written and becomes useful months later when a pattern is visible that no single entry contained.
Logs also survive better than reflective journals, because writing three lines requires no particular state of mind and can be done on a bad day.
The reading rule determines what gets written
Every tradition takes a position on whether entries are reread, and the position shapes the content more than any prompt does.
A journal expected to be read, even by its author, is written with an audience in mind, and the writing becomes more composed and less candid.
Practices aiming for candour therefore either forbid rereading or dispose of entries, which sounds wasteful and is the mechanism that makes honesty possible.
Why most attempts stop
Journaling habits usually fail through ambition rather than disinterest, when someone sets a standard of length or quality that a normal day cannot meet.
The gap between the intended entry and the available energy produces a missed day, and missed days accumulate into abandonment.
Formats that survive set a floor low enough to be met when tired, which is why the durable versions specify a small minimum rather than a good entry.