A gratitude journal that survives past the first week is usually a small one. Three lines, not three pages. The ambition to write a profound daily reflection is often exactly what causes people to quietly abandon the habit by the second Friday, once the novelty of the idea wears off.
What helps it stick is specificity. Writing that you are grateful for family in general rarely lands the same way as recalling one particular moment, like a sister calling just to talk. The more precise the memory, the more it seems to register, because the mind is recalling a scene rather than filing a category, and scenes are what memory actually holds onto.
Timing matters too: attaching the habit to something already automatic, like the last few minutes before switching off a lamp, helps it outlast a habit that depends on remembering to start fresh each day. None of this needs to feel like self-improvement homework, since the quieter aim is simply to notice, more often, what is already going reasonably well.