There comes a point within a manuscript's life cycle where it loses its shiny luster. Sometimes, it's because we've been working on the manuscript long enough that there is nothing new in it for us to discover. Or maybe we've gotten stuck and have no idea how to move the story forward. Or perhaps we've hit a scene that we just don't want to write though we know it needs to be there.
Regardless the reason for why the manuscript now seems dull to our imaginations, that will be when a new shiny bauble dangles in front of us, distracting our brains from the story we are meant to be working on.
Some writers will chase the new shiny, but following every shiny, new idea can lead to the road filled with incomplete manuscripts. There is one thing that all successful novelists have in common: They finished a manuscript.
As such, every writer wishing to pursue publication needs to develop the discipline needed to persevere on a manuscript that has lost its shiny-new luster.