Most people consider writing to be a fairly anti-social activity--which, in most cases, it really is. You spend most of your time hunched over a computer screen or a notebook, scribbling or typing away. Countless hours are spent alone, editing, writing, or re-drafting.
But there is an inherent need to socialize as well. After all, a majority of your customers are going to buy your book not only because they like the look of it, but also because of YOU.
I spent the weekend at San Diego Comic Con (a totally epic weekend, by the way), and I noticed an interesting phenomenon: the most popular people were the ones who were kind, friendly, and outgoing.
For example, I sat near a fairly well-known comic book artist. He greeted every single one of his customers by name, gave hugs, took pictures, and interacted. In the four days of the convention, he ALWAYS had people by his table.
Compare that to other artists who were sitting and either drawing or just waiting, and their sales were probably much lower. Their clients were far fewer, and the interactions were much less pleasant.
I also met amazing Australian thriller author Luke Romyn. He was one of the friendliest people I met at the entire con, and I know his personality is a huge part of what has made him incredibly successful in a highly competitive industry.
The same goes for the Winner Twins, authors of the epic science fiction series The Strand Prophecy. They talked with EVERYONE, and they were so nice about interacting both with their die-hard fans and their new recruits.
Remember, everyone is trying to sell something. As an author, you're trying to market yourself to people who have never heard of you. You can't expect them just to like your product, but you have to "sell yourself".
You know how I got people interested in what I was selling? I offered "free" high fives all day long. It put a smile on people's faces, and when I started talking to them, they were much more interested in what I had to say.
If you want to succeed, you have to be social, friendly, polite, and outgoing. It's the only way you'll make it in this highly competitive industry--or in ANY industry!