To get a book underway, you have to fully commit to it.

This is less obvious than it may seem.  One of the hardest parts of starting a book is committing to an idea.  Because ... what if the story isn't big enough?  What if it isn't compelling enough?  What if there isn't enough of an arc; what if it's the wrong perspective; what if there's a better way to tell the story?  (Or should you be telling another story altogether?)

Committing to a story can feel almost as momentous as getting engaged.  The questions you ask yourself aren't so different.  Willl I really be able to live with this person day after day, year after year?  I really like X about him, but I can't stand Y.  Things I like about him in small doses might become intolerable over time. And how will he age?

In an interview in The New York Times Magazine, Philip Seymour Hoffman addressed this issue of committing to an idea.  He was talking about how he starts from scratch every time he becomes a new character, but it struck me that the creative process he describes is similar to a writer's. "Creating anything is hard.  It's a cliche thing to say, but every time you start a job, you just don't know anything.  I mean, I can break something down, but ultimately I don't know anything when I start work on a new movie.  You start stabbing out, and you make a mistake, and it's not right, and then you try again and again.  The key is you have to commit.  And that's hard because you have to find what it is you are committing to."