There have been a few exceptions...but for the most part, you only get one chance to make a first impression. Stated another way, you can only be a variable when you're actually a variable. If you don't have a sales record, publishers have to rely on a set of complicated formulas--and possibly their tea leaves--to determine how much your book is worth...Her point (which I totally agree with) is that you should be careful how you debut and whom you debut with. Don't jump at the first small press or self-publishing option you get without really thinking about it. People generally put more value in unknown potential than they do in someone who has a record we can look at. Publishers and the reading market are not immune to this. (This has recently become an additional reason for me not to jump onto Kickstarter with my beloved-but-rejected novels. Not yet, anyway.)
But once you have a sales record, it will follow you around for the rest of your career. Publishers no longer have to guess how much your books are worth; your sales figures will tell them.
However, I would submit that you're more likely to write a bestseller in your 3rd or 4th or 10th book than you are in your first. I'm basing this on the fact that many of the bestselling novels I know and love were not debut novels:
- Orson Scott Card. Best known for Ender's Game (1985). It was his 8th published novel.
- Suzanne Collins. Best known for Hunger Games (2008). It was her 8th published novel.
- Scott Westerfeld. Best known for Uglies (2005) and Leviathan (2009). Uglies was his 8th published novel (dang, a trend!).
- Brandon Sanderson. Best known for Mistborn (2006) and his contributions to the Wheel of Time series (2009+). Mistborn was his 2nd published novel.
- Neil Gaiman. Best known for Sandman (1989+), Neverwhere (1996) and a bunch of other stuff. But his first published novel was co-written in 1990 and he'd been writing graphic novels since 1987.
- Chuck Palahniuk. Best known for Fight Club (1996). This actually was his first novel, but according to Chuck it "was a huge failure" and the film (released three years later) "was a flop."
My point is that, yes, your debut is something special that you should take care of. Don't squander it the first chance you get. BUT if selling stories is something you really want, don't stop writing. Ever. No matter how you debut, no matter what publishers or the market thinks of you, there will always be a way for you to get new words to your readers. There will always be a chance that the next thing you write could be The One.
Statistically, the more you write, the better that chance gets.
* Krista and I were on surprisingly parallel querying-agent-submission paths for about a year or two, before she got a book deal and I got a job.
** Maybe not "failed" so much as "didn't hit it ridiculously big."