Now I understand this, and I think I know why it makes sense.
The urge to write is an addiction. Once I start on a book, I have a need to write the next line, the next chapter, the next sex scene, the next conflict...you get my drift. It's a driving force that I can't quite put into words. My mind is wrapped in the story, how I want my characters to act and feel and how I want the story line to unfold. Writers absorb everything like a dry sponge. Outside influences can ooze into the places of our mind and dirty-up our story. I've told everyone around me that anything they say or do can be "used" in a book. I've written characters around one person. I have a list of people I'd like to use as a villain. I consider this a challenge, writing a real person into my book and then "faking" them up enough so that they're a "real" character. Does that make sense?
Okay, back to writers as loners. I'm not saying that we are anti-social (some writers say they are). We just like to be left alone. When I have the urge to write, I want to ease that desire instantly. There's nothing worse than "needing" to complete a scene and you're interrupted. Sometimes it's difficult to dive back into your scene. Ever been disturbed during sex? So, you know what I mean...
I compare the insanity of the writing addiction to the strong urge to pee. If you hold it long enough, the urge slowly turns into pain. Then when you finally release the pee, it's a tingly sensation that feels a lot like an orgasm.