Art often is about/driven by self-expression and I agree that this should be among a young (or even old) artist's driving forces to create. However, it's foolish to think that art and self-expression can exist in a vacuum without an audience and that be totally fulfilling. If you only share your self-expression with yourself, it can feel kind of masturbatory.
It's not satisfying to create art that just collects dust afterwards. Maybe Dada would put on a ballet show for an audience of no one but we should acknowledge that art, from writing to dance including everything in between, almost universally relies upon an audience as much as a creator. What can you really effectively express if you only express it to yourself? Art is a conversation and writing is and wants to be part of that conversation.
I see a lot of the time that "you should write just for you!" and yes you should do that but that aphorism also puts this idea into heads that "you shouldn't want or need an audience to feel good about what you create," which I think falls a little far from the truth. I write great poems that I love but once I write them, I also want to share them with people. And it's natural and understandable to have that desire and feel irritated when the literary structure/canon/environment in which you write is never going to embrace you -- I still write, sure, and I find people to share things with -- it shouldn't ever stop someone from creating -- but tell you what it sure can do is knock the wind out of your sails a little.