Novel writing is a novel profession. Isolated. Quiet (except inside one’s head). Consuming. The only similar profession I can think of may be that of a painter – the artistic kind, not the house-painter type. But I don’t know for certain…perhaps there are others.
With most professions, there is interaction with at least one other person as the job is being performed. Doctors couldn’t do what they do without patients by their side (although now I’ve heard they can diagnose virtually – still, they need a person). Lawyers need clients, machinists need customers, ditch diggers wouldn’t be digging were it not that someone requested the job done. Even actors require an audience – people to approve of a stage performance or another person with whom to interact (even Tom Hanks needed a camera crew to film his solitary performance in Castaway).
However, writers (and artists) don’t need that. It’s preferable to have patrons or fans, but that comes AFTER the fact – a writer has to have written something in order to accumulate fans. But unlike a lawyer, who will need to build a clientele in order to survive, a writer can (and does) produce his or her work without the promise of things to come. We write in solitude, submitting our work to the ether with the hope but never the promise of distribution and accolades. We have to. We know no other way.