Talking about the difficulties of estimation. At least he managed to publish a few books. Imagine that he waited to publish anything until the complete work is finished. Sounds familiar?
Beyond that he released a number of them in rapid succession. For a while there the ideas must have just been coming as quickly as he could jot them down. Then, for those who are in the know, he quickly ran into an issue where continuing the plot threads he had setup all came to a confluence point where decisions needed to be made before he was prepared to do so.
From what I understand extensive revisionary work was done. Entire sections and chapters of the story were rewritten to accommodate for the new trajectory for the adjusted plot lines of various involved characters. And, this is my least positive memory of all of this, he actually brought in some outside help to ensure he was capable of undoing what has been dubbed as the "Meereenese_Knot":
https://gameofthrones.fandom.com/wiki/Meereenese_Knot
For a less "as far as my terrible memory can remember" version of what I explained above here is a quote:
> "The first three novels each came out within two years of each other, in 1996, 1998, and 2000 respectively. However, it took another eleven years for Martin to write the fourth and fifth books, A Feast for Crows (2005) and A Dance with Dragons (2011). Partially, this was because A Feast for Crows and A Dance with Dragons were originally one novel, which grew so long that author George R.R. Martin later decided to split it up into two books (the events in both happen concurrently but follow separate characters)."
Three novels from 1996 to 2000. Another 11 years for the next two. Here we are, patiently waiting, for the 6th book of the series, "A Dream of Spring".
Of course the majority of people loudly banging their shields complaining about Martin's lack of shipping have probably never undertaken the task of writing a feature-length novel before. I'm sure an even more comical percentage of those have actually released a multi-art series with anywhere near the outrageous amount of characters, named placed, and other in-world lore or detail that make G.R.R.M.'s work feel so "real" and "lived-in".
I know I've never sat there while reading only to think, "Oh, there's this many more pages before it's done? This is such a boring slog." Entertainment is a word that I feel falls short of describing the type of enjoyment I get out of the Game of Thrones series.