People seem to legitimately hate Game Of Thrones Season 8. Not everyone, of course, but as with all things, the more vocal the criticism, the more that element believes their opinion to be the only one that matters. As such, the conversation around the penultimate episode of the final season has been shaped very consciously around Dany's turn to the Mad Queen.
Some loved it. Some thought it was the natural conclusion, even if they'd have preferred a happier ending. Some simply revelled in the majesty of the spectacle. But there are others who took Dany's massacre of King's Landing to be the final straw for a show that has (allegedly) wilfully ruined character arcs in the interest of getting a cheap reaction.
To suggest that there was no precedent is utterly baffling. So too is the idea that we weren't always headed this way, and looking at the books, the show and the fandom, there's a very important discussion here about why Dany became the Mad Queen, how it happened (and how it was planned all along) and why some fans took it so badly...
9. It's Going To Happen In The Books
While it's true that the show has diverged from the books A LOT in the last few years, the places these characters end up is, in many cases at least, going to end up being the same. George R.R. Martin gave David Benioff & D.B. Weiss the broad strokes of where his story is going a few years ago, and while there'll be plenty of differences along the way, many destinations are shaping up to be the same as they will in the novels.
Daenerys is one such example. For anyone thinking this is purely the invention of the show and a betrayal of the character, then it's worth noting that Dany burning the s**t out of King's Landing is almost certainly going to happen in Martin's books, if and when he finishes them. The author has already laid the groundwork for this in Dany's arc, including passages such as this passage from A Game of Thrones:
"But it was not the plains Dany saw then. It was King’s Landing and the great Red Keep that Aegon the Conqueror had built. It was Dragonstone where she had been born. In her mind’s eye they burned with a thousand lights, a fire blazing in every window. In her mind’s eye, all the doors were red."
Or this one from A Dance With Dragons:
"The stream will take me to the river, and the river will take me home. Except it wouldn’t, not truly. Meereen was not her home, and never would be. It was a city of strange men with strange gods and stranger hair, of slavers wrapped in fringed tokars, where grace was earned through whoring, butchery was art, and dog was a delicacy. Meereen would always be the Harpy’s city, and Daenerys could not be a harpy. 'Never', said the grass, in the gruff tones of Jorah Mormont. 'You were warned, Your Grace. Let this city be, I said. Your war is in Westeros, I told you. No. You are the blood of the dragon.' The whispering was growing fainter, as if Ser Jorah were falling farther behind. 'Dragons plant no trees. Remember that. Remember who you are, what you were made to be. Remember your words.' 'Fire and Blood,' Daenerys told the swaying grass."
The books are definitely building to a conflict between Dany and someone in King's Landing, but one crucial difference is that it won't be Cersei. She's not going to be the major endgame character she is in the show, and it's likely that, in The Winds of Winter, power in the capital will be assumed by Young Griff. Daenerys is eventually going to make it home, believing herself the destined ruler of Westeros and thinking the people will welcome her with open arms, to find that another Targaryen (or at least, supposed Targaryen) has taken the Iron Throne she so desires. Her arc has already signalled a decent and a willingness to do what it takes, and she's going to end up lighting King's Landing up as she takes the fight to (f)Aegon. It may be slightly more accidental - the stores of wildfire we saw in The Bells are likely to come into play there too, and could be how the destruction really happens - but the endpoint remains in a similar area.
Another crucial difference is in timing: in the books, it's quite likely the order of events will be reversed - Daenerys spirals downwards, burns King's Landing, and THEN goes North to fight the Others as an act of redemption (and possibly even sacrifice). That gives it a different context, but it nonetheless means Dany burning KL was something Benioff and Weiss were surely told about by Martin and had to include in some way.