I think they should really force themselves to start with short stories first; focus on finishing a story. That avoids a sunk cost, avoids people beating themselves up for what they believe is their life's work getting rejected by publishers (for e.g. being too long), etc.
Same with software development; it's easy to write big chunks of code, it's hard to get that to production.
[0]http://centerforfiction.org/awards/the-first-novel-prize/
Writers are also told it takes two or three failed novels to write a good one.
And on top of that, there are plenty of writers whose primary motivation is vanity. They care more about seeing their name on the spine of a book - as if that proves they're Someone Important. They also think the more words there are, the better they're doing, and don't understand the value of understatement or editing.
Writers who view it as a business - willing to learn the required skillset, realistic about their potential, and with a product plan, a marketing and customer engagement plan, and a realistic assessment of sales outlets and likely income - are not common.
I am a pretty avid reader and would never pick up a novel by a first time published author that is 800+ pages; the time (and potentially monetary) investment is just too large. On the flip side, I do pick up books by new/unheard of to me authors that are 250-400 pages long.
I also remember there are companies that allow you to publish and sell your work, and handle the printing and shipping. I don't remember the exact companies, but that sounds like a good fit for the poster.