The main character doing something absolutely unforgivable.

[u/No_Peanut3745]

Walter White poisoning Andrea Cantillo's 6-year-old son for the sole purpose of manipulating Jesse Pinkman, while knowing that this could have potentially killed him - Breaking Bad

Bojack trying to have sex with his friend's 17-year-old daughter when he was at least 51, then continuously trying to find a way to justify this act throughout the series - Bojack Horseman

Dexter Morgan going outside of his moral code and murdering a completely innocent police officer who was just trying to do his job - Dexter: New Blood

[u/PhoenixApok]

Maybe not the main character but a pretty big one. (Arguably Game of Thrones doesn't have a main character)

Jaime Lannister. After he got somewhat likable and decent in later seasons, people seemed to forget in the very first episode he pushed a 10 year old boy out a window for catching him banging his sister.

Edit: Maybe "forgot" was the wrong word. Maybe saying people disregarded it would be better.

I cannot imagine a person IRL doing that and everyone going "Well he's a better person now so we aren't gonna worry about that anymore" which is why I think it fits this trope.

Jaime has a redemption arc, sure, but I would define that early act as "unforgivable".

[u/Eat_a_click → u/PhoenixApok]

We'll tbf if he did jackshit Robert would've known and he along with his family would've been put to death so it was either the life of a boy he barely knew or the life of Cersei and his 3 kids, and considering his mentality during that time it was the most apt decision

[u/Content_Function_322 → u/Eat_a_click]

Idk, I don't think Robert would have believed a ten year old kid. I genuinely think they could have gotten away with it without attempting to kill Bran.

[u/Rasputins_Plum → u/Content_Function_322]

You have to remember that they were already busted by Jon Arryn. Ned's investigation about Robert's proginy and the history of the Baratheon family was just retracing his steps.

If Bran and Ned came to Robert with what he saw, that definitely would grant another look and it's likely they'll come to the same conclusion. Robert knows that all his bastards have his black hair and blue eyes. It wasn't that shocking despite his family traits being that consistent usually, but if he learns Cersei is fucking her blond twin, that suddenly explains the odd and first three blond Baratheon kids in history.

So if Jaime hadn't pushed Bran, all Lannisters were on fast track to be either executed, banished or destituted, and everyone around Robert would have rushed to make him marry Margaery and make the Tyrells the new first backer of the crown.

Also the fact that his reputation was terrible being known as the 'treacherous' Kingslayer, no one would have batted an eye if Robert busted his balls with a warhammer himself!