The Bullet Journal combines calendar, to-do list, and journal. A bullet journal can help you be more productive and organized. Writing things down helps you to focus on what is important. Rebecca Greenfield at Bloomberg reports that David Allen, the author of Getting Things Done, says, "Your head is for having ideas, not for holding them. If your head is still wrapped around food you should've bought this morning, or the last meeting you were in, you're trying to use your head as your office. And your head is an absolutely crappy office."