Disclaimer: I'm not a literary agent. I don't really know what they think, beyond the thoughts they put out there on their blogs and Twitter feeds. (I do not listen to the haters who think agents are an elitist clan of devil spawn who take joy in crushing the dreams of aspiring writers.)
But I think they would agree with the title of this post. Let me explain why.
First, you have to understand humility. Contrary to popular belief, it isn't beating up on yourself. It isn't saying your writing is crap, especially right after someone has complimented it. It is not a lack of confidence. I grew up with this simple definition:
HUMBLE = TEACHABLE
You can definitely believe you know a few things while acknowledging there's room to know more. I have a student who epitomizes this. With all her accomplishments, she could easily have the biggest head on campus. Yet bragging would never occur to her. She does what she does, no big deal, but if you compliment her, she'll thank you.
She doesn't tell you all the reasons why your compliment is misplaced.
So, why do I suspect agents find humility sexy? I'm sure they want confident writers who believe in their ability (well, most of the time—we all have moments of doubt) and don't have to be talked down from the ledge every other day. Confidence is not the opposite of humility—arrogance is.
We've all seen arrogant aspiring writers (and, er, some published writers, too). The ones who lash out at anyone who dares criticize their masterpiece. Who insist it's your fault for being dense if you can't keep track of their fifteen different narrators. Who don't care if you tell them word counts much over 100k make publishing pros twitchy—not a single word can be cut from their 450k-word debut thriller. Who say they will never change X about their novel (title, character's name, their vision of printing the whole thing in Comic Sans) no matter what a publisher says.
It ain't sexy.
(Okay, those were extreme examples, but even when you scale them back, I'm thinking they're not too attractive.)
Humble writers do their research on the publishing industry and don't blame 'the system' for all their problems. They handle critique like a pro, not giving in to every beta reader's whim, but being open to possible improvement. They'll aspire for greatness, knowing there will always be more to learn, and never claiming they've already arrived and why haven't you acknowledged it yet?!
Is there anything that helps you find the balance, neither tearing yourself down nor puffing yourself up? Taking the stings of critique and the occasional right-hook of an agent rejection without letting them destroy you? Taking compliments and accolades without thinking you've arrived at the top?