​Sometimes (maybe often), a big or ambitious writing project can suffer esoteric emergencies.
A writer might experience a crisis of confidence (or might suddenly birth a punitive inner editor). A writer might experience a crisis of interest (an initial effluence dries up). A writer might experience a crisis of life’s mundane (or monumental) messiness.
Broken confidence, eclipsed interest, and interrupted work are annoyingly inevitable. Sometimes it’s pretty easy to ensure a project’s survival (if, by “pretty easy,” we agree to mean “biting a stick and bearing down through streams of sweat and tears”).
But sometimes these crises, when left untreated, threaten survival. For big, ambitious writing projects, there is no inoculation (for either project or writer), but a little preparation and a lot of triage can ameliorate some damage.
Preparation (if you’re like me) means: 1) reading the books on maximizing creative productivity, 2) prioritizing/scheduling your time, and 3) “mastering” the enigma of a balanced life. Also 4) making spreadsheets, to-do lists, and/or bullet journals (that will eventually/inevitably mock you as you miss deadline after [self-imposed] deadline).
Preparation is important, of course, but it’s probably best understood in the service of endurance (not success).
Triage is different, though. Triage helps you identify and treat your project’s emergent issues…and it’s actually more effective when it happens after you realize your project is gasping for life and in need of an SOS.
Triage often involves sending a particularly ill part of your project to a trusted friend—a good thinker with a respected readerly opinion (who will refrain from offering excessive and/or grad-school-style critique)—or to a smart, detached professional.
Who is this trusted confidante? Hard to tell! But merely sending a project out into the world forces it into a new environment where you can better diagnose and treat its problems. In some ways, it almost doesn’t matter if you reach the exactly right person.
Of course, in other ways, the exactly right person is much better than any old person, so take the opportunity to ask for a short evaluation. What works, what doesn’t, and what’s their best advice for treatment? Whether or not the you receive practical help,  you’ve at least narrowed down your second-opinion pool.

The bad news is that for most writers, there’s is no cure for a big, ambitious project. It’s more like pyrotherapy: The fever must run its course. Help it along by finding the most effective treatment to minimize your pain and maximize your project’s vitality.