I don't know the ending, even when I know the ending. In every book I've known the ending more or less, but a crucial variable is missing from the equation as stated; namely, the characters.
I wrote a book that was a fantasy re-telling of Verne's A Journey to the Center of the Earth. I already had the ending. The characters return to the surface via some sort of eruption, tumbling out into a place initially unfamiliar. It was there in the book and there in the movie. But knowing that much was barely even a starting point.
I could not possibly write that ending without knowing who came tumbling out. What sort of people were these? What had they gone through? Did the group lose anyone along the way? All questions crucial to the telling of the story, so there's no way to write my way toward it. I had to discover my way to it. And that was the joy and the heavy lifting of the work itself.
The write every day bit is solid. It's the Jerry Seinfeld calendar method. I'll append an alternative. I write four days a week. But I *always* write four days a week (or have over the last ten years, with exceptions for illness and family events and the like). It almost doesn't matter what the routine frequency is, so long as you stick to it.
As for having the courage of your convictions, that's fine if you've got 'em. How about the courage of my doubts? I question everything about every story I write, and if I happen to re-visit an earlier work, I come up with new questions. Convictions? Oh, steer me to the nearest Conviction Store, please! I'm just trying to get a story told.
I say all this not to throw shade on H. Mantel, but to say to other writers, if it feels like they're talking about someone else, about established writers, or a different style of writer, you are not alone. That's the thing about advice. For one person it rings false, or irrelevant, and to the very next person it is profound and illuminating. It's why I read all this sort of advice, whenever I happen on it (I no longer go looking, though). Because even the advice that did not resonate last year might turn out to be valuable to me this year.