Some things, like school, work, chores, and the like aren't exactly optional. What you do in your spare time is, though.
What I usually do in my spare time varies, sometimes. I like to read, sometimes I write blog posts, and sometimes I write. :)
It's not always easy to sit down and force yourself to get in your 100 words, your 1 page, or whatever your daily goal is. Actually, it can be tiresome.
That's when you have to make the decision to write.
You don't become a writer when you go to your first conference, get 100 hundred likes on Facebook, or even when you get your first book published.
You become a writer when you decide to write. When you write Chapter One when you reach 30,000 words, when the voices in your head just won't stop pouring out onto the page.
Don't call yourself a writer.
Make the decision to be a writer.