What I'd meant to talk about was a fairly narrow (if possibly widespread) issue of allowing a new idea to distract you from an existing one while in the middle of a writing project, specifically a novel-length project. This is a common enough symptom of muddle-in-the-middle, wherein about a third to halfway through the writing process, the manuscript feels tedious, pedestrian and boring. Your subconscious is looking for excuses to bolt at that point. Many if not most writers go through that experience. The point I was after was not to let the new shiny pull you off the current project. That's bad discipline, and as you can neither revise nor sell an incomplete manuscript, it's bad for your career.
I myself have dealt with this. As I said to Kelly in comments:
And to be clear, I have one major unfinished novel that's been on my desk for the better part of the last decade, for exactly the reason you describe. (It's Original Destiny, Manifest Sin.) At that time, I didn't have the professional tools to finish what I started back around 2004. But I didn't abandon that novel because I had a better idea — which, you'll note, is specifically the issue I address in the post — I set it aside until my professional development as a writer let me come back to it. And ODMS is the next novel on my writing schedule after I wrap the Sunspin cycle.
Original Destiny, Manifest Sin was simply beyond me at the time that I began writing the book. That's perhaps the strongest novel idea I've ever had, but needed me to be a stronger writer to address it. As I've observed elsewhere, I realize a while back that in some important senses, the entire Sunspin project is a warm-up for returning to ODMS. This has to do with my control of structure and character in a highly multithreaded storytelling environment.
Likewise, back to my original point about stopping work, there are life crises that represent a legitimate and even necessary halt to writing. This was discussed by
My point being to clarify yesterday's post — sometimes there are reasons to abandon a project. Simply falling in love with another idea is very rarely one of them. Discipline is still important, critical even, but as I've often said, there is no canonical writing advice except "write more". "Finish what you start" is pretty high up on the list, but it's still context dependent.