After spending a few thousand hours talking to characters in your head while you write a book, it's difficult to give them up and send them off to play in the big outside world.
You live with them day and night. Sometimes they invade your dreams. You imagine their sex scenes while you're driving down the road or loading the dishwasher. A stray overheard comment leads to an new way of resolving their conflict.
And then, suddenly, they're gone. Their story is finished and packed off to your editor and you mourn their absence for a couple of days before you dig through your files and begin a new story.
Eventually, you'll receive edits on your submission. This time as you make corrections and revisions, its more like a short visit with old friends who inevitably leave, instead of a that initial wrench. You wave them off a lot more cheerfully with anticipation and relief.
Months later your final line edits show up. By this time, you're frowning as you try to remember who these characters were. You're head is filled with so many others already. You skim through your book to refresh your mind. Oh yes, you think. I remember this.
Final line edits are finished and off your story goes for the final touches--the cover and blurb, the excerpt and dedication. And a few days later, it's for sale! People buy your book and meet those characters that you lived with so long ago.
Are they real? Absolutely. For a while.