I recently finished a writing pedagogy class, where I discovered why journaling works. You see, writing isn't just a means for documenting thought; it's also a way of learning (epistemic writing). When we write, our thoughts spin out in a web, which allows us to make certain discoveries. Through journaling, which is personal and less-hindered, we are able to make self-discoveries. I had a professor who once said, "reality is a function of language," which to me means that through a shift of view or expression, the world can appear in many different ways. When journaling, we are able to view the subject through lenses into alternate "realities."
Originally, I purchased the plain black journal to help me decipher a few puzzling occurrences that were seemingly paranormal. I craved perspective. My writing took me down a different path, however, and I haven't looked back. At the start of 2013, I couldn't have anticipated how difficult the year would be. I journaled through my the uncertainties of my first year of college, my crumbling family-life, the illness and death of someone very close to me, and my own health concerns. And through that, I found love, and I journaled that too with a shaky pen and a thumping heart.
I would encourage anyone to pick up a journal and start writing. It doesn't have to be "spiritual," which was the intention of my own. You will see a difference in yourself.