In terms of character development I think the best moment for me was:

When young queen Cersei meets the which fortune teller, we get to see her character develop, as a young noble person she’s rather cavalier with other people’s time attention and lives. Thinks nothing of threatening the witch

I liked how dense the prediction was, it tied a lot of the rest of the story together, the king will have 20 children but none of them with her, she will have three. This upsets her, but she internalizes it, and it becomes a motivating factor for her personality.

https://www.youtube.com/watch?v=_6kQJ9HPpQ4