Why do some novelists use surname for their main character while other uses just their first name?

I was reading a novel and I noticed the author uses the first name of the main character throughout the novel. In another novel, he uses a surname for the main character throughout the book. I noticed this pattern in several other novels from other authors. What usually decide this factor? Is it just the author's choice or does it depend on the genre, the plot, the character's sex?

Why do some novelists use surname for their main character while other uses just their first name?
While it can be a matter of choice, some genres have a kind of "culture" about names. Military-ish sci-fi would be more likely to use last names, for example, because addressing people by last name is common in the military. Take a look at the details of a novel (type of genre, demographics of it's fanbase, author's real world experiences, etc) and you may find the commonality that dictates which choice the author has chosen.
Reply:This is simply a stylistic choice and there is no right or wrong. Kafka uses an initial like "M." In news articles, you use the person's full name first then use the last name every time after that, but with novels, the choice is yours.