This also happens in the workplace and with students in academia whose writing represents high stakes in their future. The complexity of the writing process. The different stages of the writing process require an agile mindset and very different skills at different stages. This means the writer's mind needs to shift gears frequently. Using journals is not a good way to teach structure, form, or organization, but that was not my purpose.
Journals are a good parallel for Psychology class.
They are a 'non-threatening' form of writing. For students fearful of writing, getting to the bottom of the page, day after day, was a psychological victory over the page and their fears of writing. Although most students wanted me to read and respond to their entries, they could put an X at the top of the page if they didn't want me to read it. For students who were phobic of assessment, this was a relief. It helped them just relax and write.