I knew I was a writer when I would create vivid descriptions of people, places, and things in my mind as if I were writing a novel. I was young, bookish, and awfully socially awkward. I would entertain myself by creating moods, and tones, and passages inside my imagination.
As I aged, I began putting those words to paper. But the mindful activity of converting consciousness into prose never left me. I still do it when I'm outside smoking some ribs; at Walmart, people watcing as I wait hours for my car's oil to be changed; from the sweet drops of water I drink from the herd of bottles on my work desk.
That's how I know I'm a writer. It's a disposition to be truthful and honest with the world, and to make it clear through the prose of my fingers and brain.