Certainty is less secure at boundaries, reality less rigid. In places ambiguous (neither sea nor shore, day or night, river or land) magic can seep through.
“You can’t wait for inspiration, you have to go after it with a club.” — Jack London
“The road to hell is paved with works-in-progress.” — Philip Roth
If your book, fantasy or historical novel, requires combat using edged weapons, a good book to start research with is Medieval Combat, A fifteenth-Century Manual of Swordfighting and Close-Quarter Combat by Hans Talhoffer translated and edited by Mark Rector.