I actually disagree with this. Martin has known his ending since at least 2008 when he met with the fellas who adapted the series into TV. I think his problem is just that he’s allowed his series to sprawl too far in every direction.

Rothfuss is a bit more complicated since I think he knows that the ending he has always had in mind is one that will be rejected by many readers, since many readers are expecting a very specific narrative conclusion. Like, I think most of his readers are expecting a showdown between Kvothe and the Big Bad(s), but this is certainly not something that will happen or something Rothfuss ever intended to happen. But it leaves him in a difficult place because of the success of the series. He wants to please his fans and give them what they want but isn’t sure how to give them the ending they want based on the two novels he’s written.