As if Hilary Mantel's wise words on memoir weren't enough, she also has something great to say about the writing process itself. In answer to the question, "What’s the best thing about writing a book?" she replies:
The moment, at about the three-quarter point, where you see your way right through to the end: as if lights had flooded an unlit road. But the pleasure is double-edged, because from this point you’re going to work inhuman hours, not caring about your health or your human relationships; you’re just going to head down that road like a charging bull.
This is REALLY important for all writers to understand, and here's why:
Anne Lamott famously said, in Bird by Bird, that every piece of writing begins with a "shitty first draft." That's almost right. The reality is that most pieces of writing are built from many shitty drafts, until you reach a point where the whole thing starts to cohere and come into focus. That's Mantel's "floodlit" point, and it truly is magical.
Mantel puts the transition at about three-quarters of the way through, but I think it can show up anywhere up to about ninety percent through the process. When it shows up, though, is far less important than that you keep working until it does.