More importantly, having an agent has created this little voice in my head--this little person sitting on my shoulder as I write, now. Because a phenomenon has occurred, in the weeks since I've signed with him: I've started seeing my book (the current one, as well as works-in-progress) through his eyes. We've been through a couple of revisions together--he gives me suggestions, we bat ideas around, and I get to work. And now, as I write fresh material, I'm already jumping ahead to wonder, "What will he think of this plot twist? Will he agree that her reaction here is appropriate?" I'm already anticipating his input, his suggestions.
Sure, that voice can be a little irritating, because I'm not used to it being there. I've only ever had to please myself when I write. But now, there's someone else (and hopefully, in the future, many more someone else's (readers!)) to consider. And I've realized--having someone else to please has also done something wonderful. It's upped my game. That agent on my shoulder is like a supportive coach, holding the goal up, higher than it's ever been, and telling me, "You can do it. Reach higher, go bigger. Stretch yourself."
Sure, one could argue that as writers, we should only please ourselves. That we should ignore other voices, the tendency to please someone else. But, as long as we agree with those suggestions of another, as long as they do nothing but improve the book, why not try to please them?
So, even if you don't have that agent just yet, place that little coach on your shoulder anyway, the one telling you to reach higher, go bigger. Stretch yourself.