If you're a certain type of actor, then eventually stepping into a director's shoes is a natural transition. I've always been the actor who's very focused on the narrative, where my character is in the story, and how I can benefit the story. I've always had a technical aspect of what the lens is, how the camera is going to move, how I can feed the information the director applies within that move. If you're that type of actor, narrative-based, technically proficient, the next step is actually not that far.