Because it is important to write things no matter how pre-conceivably irrelevant they are. Because it is important to chronicle life, no matter how short it is, through thoughts and musings and poetry that blossoms from your temples. Because memory is not something that you can trust and that you need tools, like writing, to preserve significant details brain cells might fail to remember. Because what you say will always be relevant, not to others, but for you alone. . Because you need to, for yourself and not for anybody else.
Therefore, write. And never stop.