We all have enthusiasms, things we like. Football or opera, video games or cooking, volcano watching or organic gardening -- we all have something that we like to do or learn about. If you are fortunate, your enthusiasms correspond roughly with how you spend your time. Better yet, you may be lucky enough that someone actually pays you to pursue your enthusiasm. Some people, unfortunately, have unhealthy enthusiasms. I don't doubt that narcotics are tons of fun to take -- why else would anyone take them, as Irvine Welsh explained -- but just because something is fun doesn't make it healthy, and it doesn't mean that the enthusiasm will even stay fun. Enthusiasms can be unhealthy in terms of the actual harm it does to body and mind, but also by pushing aside other things in life. We all know this.
I have recently concluded that novelists are people with unhealthy enthusiasms.
I don't mean that all novelists are necessarily using prodigious amounts of drugs or anything, although that is not exactly unknown. I have simply concluded that voluntarily producing a written work of novel length requires the author to be in the grip of an unhealthy obsession. That obsession need not be "to write a book." In fact, I suspect that simply wanting to write a book, no matter how fervently, will not propel anyone through the ordeal of actually, you know, actually writing a book. The object is simply too diffuse to propel the writer onward.
The would-be novelist requires an unhealthy enthusiasm, an utter obsession in something more specific than a longing for completing the work. A novelist needs an unhealthy enthusiasm with telling a story, with playing with an idea, with expressing a point of view, that simply removes the option of not writing the novel. To have written something is pretty cool, but the actual process of writing inevitably degrades at some point in the process. Some times along the way, the words won't come, the characters won't ring true, and the plot will fall apart. At those points, the entire ordeal will be considerably less fun than mopping the kitchen floor, changing the oil in the car, or getting a filling put in by the dentist. If you can stop writing, you will. Period.
Not finishing the novel you think you want to write may not be a sign of your laziness so much as an indication that you are actually able to function as a mostly normal human being. So don't beat yourself up over all those barely begun books on your hard drive, because your family, pets, and personal wellbeing are likely the better for your abandoning the projects.
Me, I can't stop working on this damn thing.