Game of Thrones has made more episodes than the books' author George R.R. Martin could keep up with, and instead of pulling the plot from the existing fantasy series, it is now up to show's writers to decide the fates of the characters. As Martin works on the next book, the sixth in the series, he has relinquished control of what happens on the Game of Thrones TV show to its showrunners, David Benioff and Dan Weiss, they recently told Entertainment Weekly.
Season six is the first time that the show will produce episodes not based on what Martin has written, but he did give his input as to how the series should play out, and revealed (back in 2013) to Benioff and Weiss three major "WTF" moments that are to be included in the TV series. "Showrunners David Benioff and Dan Weiss tell EW those conversations included 'three holy sh– moments' in particular." We have seen two of them so far.
The first: Stannis Barathon trading the life of his daughter Shireen for some promised good juju that he ultimately did not receive. This incident was shown during season five, and has not (yet?) happened in the books.
The second: Discovering Hodor's extremely sad origin story that somehow makes you like him even more.
The third: ????
Showrunner David Benioff teased that the last big surprise is "from the very end."
Benioff and Weiss also tell viewers (who are worried that watching the show will spoil the books) not to fret. Although there will be some plot overlap, ultimately the book series and the television series will be going in different directions. Benioff tells Entertainment Weekly:
People are talking about whether the books are going to be spoiled – and it’s really not true. So much of what we’re doing diverges from the books at this point. And while there are certain key elements that will be the same, we’re not going to talk so much about that – and I don’t think George is either. People are going to be very surprised when they read the books after the show. They’re quite divergent in so many respects for the remainder of the show.
And finally, for the first time, your friends that read the book can't spoil what is going to happen on the show for you.