Putting down your thoughts into paper, is an easier way of articulating your thoughts, feelings and needs. Most children are raised in an environment where speaking up on those feelings and acting on them is a crime or a taboo. Nothing comes easier these days. We are brought up to listen and do as we are told and not question the relevant authority or there will be consequences.
So far, you have to grow up and leave home eventually. You start living in an environment where people speak their minds out. Sometimes people view you as shy or weak person who can't stand for his or her rights. They don't understand the nature of the environment in which you grew up in. It weighs on you even without knowing and relationships become strained because you're closed off and every time you want to put a step foward something always holds you back.
The guilt that manifest when you try to share your thoughts and feelings. Therefore you prefer silence. Then you become that person that no one tends to notice and you are swallowed by all your thoughts inside your head. You're only friend becomes the voices inside your head and maybe that's why many are suffering from mental illness because they were never taught how to SPEAK OUT.