Unfortunately, a lot. The right name can make a character lovable, vulnerable or distant. You could name the main character Hugo, Elmer or Jackson and even though it is the same character with the same issues, it will bring up different things for different people. In their lifetimes, most people only have to come up with names for a couple of kids (unless you're John and Kate), a few cats, a dog or two and miscellaneous goldfish. Writers have to come up with names for all of the characters in every book, main or not.
I say 'come up with' loosely, because it's more a process of deduction than creation. My characters seem to already have names and it's my job to figure out what they are. I tend to use my kid's elementary school directory for clues. I get a feeling for a character and try each name on - actually say it out loud to see if it's the right one. Is this kid a Cory or a Kevin? A Jasmin or an Emily? When you get close, the name settles down on a character like a nice winter coat that they parade around in and try on for size. If it seems to work, then I write it down in my handy-dandy story notebook so that I don't forget it. Now I have to find a last name to go with it.
I used to name characters based on names I liked rather than the names they liked. The first book I ever wrote contained a secondary character called Olivia, a name I wanted to use if I ever had girl children. Rather, I tried to call her Olivia, but apparently she insisted on being called Nina. It went on like that, jumping between Olivia when I was paying attention and Nina when I was so into the writing groove that I wasn't, until I just gave up and named her Nina for good. Now I'm a little wiser and save myself all of that "find and replace" nonsense.
On this date: In 1963, the First Baptist Church in Birmingham is bombed, killing four schoolgirls.