It's an old saying: Everyone is their own worst critic. You see imperfections in something you create because you always want perfection from yourself. Actors are not immune to this phenomenon, not even actors on Game of Thrones, one of the most acclaimed TV shows on television.
Stephen Dillane, who played Stannis Baratheon in Seasons 2-5 of the series, did not like the way he played his character. He seems particularly hard on himself in an interview with British newspaper The Times (behind a subscriber wall). EW gets to the good part of the interview with the British actor.
“I’ve flicked [the show] on [since leaving] to see if I could figure out what was going on, but I couldn’t,” he reportedly said. “Liam Cunningham [who plays Ser Davos Seaworth, Stannis’ right-hand man] is so passionate about the show. He invests in it in a way I think is quite moving, but it wasn’t my experience. I was entirely dependent on Liam to tell me what the scenes were about — I didn’t know what I was doing until we’d finished filming and it was too late. The damage had been done. I thought no one would believe in me and I was rather disheartened by the end. I felt I’d built the castle on nonexistent foundations.”
This is sad to hear from such a pertinent character. Game of Thrones is an incredibly complex story. But you would think the producers -- or even Liam Cunningham -- could give him some help before he shot his scenes. Despite Dillane's concerns, most fans don't seem to have noticed he was "phoning it in" during his performance.
If you need a refresher: One of Stannis' most critical storylines came in his final season on the show, when, in an effort to gain an advantage over Roose Bolton's army, he sacrifices his daughter, which in turn causes his wife to kill herself. After that, Stannis didn't fight much when Brienne killed him. He saw it as getting what he deserved.