I'm taking a non-fiction creative writing class this semester and on the very first day my professor said "most of us who write, write to understand." And nothing has rung more clear to me as a writer than that. Even people who don't necessarily consider themselves writers, still write to understand. For many people it is the only way our brains process our experiences. It's how we make sense of the world. 

In our heads everything is one giant jumble that could all be in binary for the extent to which we understand it. But when we take the time to find the words to write down about it, those incoherent feelings and thoughts running around somehow become put together thoughts and reasons that all of the sudden have some sort of significance. 

Ernest Hemingway said "write hard and clear about what hurts." He meant this as serious piece of advice because writing deeply about the things that really hurt you or even just things you feel, allows for you to discover what you got out of an experience or maybe offer up some sort of reasoning as to why you experienced it in the first place. If nothing else, it shows just how it affected you. There is something so absolutely necessary about writing. For some people, it may be an every now and then thing that they explore a thought or experience through writing to understand it. But for some of us, having a little notebook or a word document constantly at our disposal, is a lifeline. It's necessary for us to stay sane.