For me, it was the story of The Emperor in the Outcast dead. It's not really clear but I got the feeling that the Emperor felt like he was locked into his fate when he saw his future unfold in Kai's vision. Was quite emotional for me to see how the Emperor, A being of immense power, would have to rely on others to fully understand what he is meant to do...
This was a realy Heartbreaking moment and when the Emperor answered Kai's question while they are playing Königsmord*, that he knows, that he will die. * Sorry, I don't know the english name of the game.
The time when the Night Lord Talos came back to his home world with his brothers, then came upon an old woman who tried to touch him. He brushed her off, ignoring her. She was then killed by a guard. Later, Talos would discover that that old woman was his mother. He had forgotten who she was.
On a planet with the top 3 professions being -Murderer -Rapist -Arsonist I can't really be surprised.