Biggest mistake for GRRM are the ages of the characters and their arcs taking place so far apart and too quickly. Arya can't convincingly become a FM in 6 months and go back to kill the Freys as a 10 y/o. Daenerys can't invade Westeros because her dragons are too small, maybe he can pull some bullshit like her killing the Khals in Vaes Dothrak will magically maker her dragons bigger to speed thing up.
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