I Mexican't

kyoshi: sometimes some murder is OK

kuruk: just punch people that disagree with you

Roku regretted not killing Sozin specifically because it gave him the opportunity to come back and kill him, then the Air Nomads. His lack of decisive action led to a lot of tragedy, and so his advice was to make sure whatever he did, make sure it was permanent, or Ozai would come back.

Kyoshi regretted not moving sooner on the threat of Shin the Conqueror and waiting until he was at the very edge of Kyoshi Peninsula before actually doing anything. She allowed a lot of destruction on the continent because she didn't move fast enough. Her advice is to move swiftly instead of allowing Ozai more time to act.

Kuruk basically did nothing as Avatar by his own admission and basically just said that Aang had to do something, and not to back off of his responsibilities because it was hard.

Yangchen is complicated because, well, she isn't talking about one of her own regrets. She's the one trying to give the 'Violence is sometimes necessary' talk to Aang, because she's the best person to tell him his duties as Avatar have to outweigh his duties as an Airbender. Arguably she is the one telling him to murder Ozai, but personally I read that as more 'you need to do what's right for the world, and I am giving you permission to break our cultural rules to do that. Because I am the only person you can ask for absolution.'

She said most directly what all the others had been telling him too: Roku, Kyoshi and Kuruk all faced situations where their ideals about what they "should" do clashed with what would really do the most good (or at least prevent the most harm). They all chose their ideals over the real effects, innocent people paid the price, and they were urging Aang not to repeat their mistakes.

Tags from @veganslenderman

"Everybody knows that everybody dies, and nobody knows it like the Doctor. But I do think that all the skies of all the worlds might just turn dark, if he ever, for one moment, accepts it."

I really like how the scientology speedrunning trend is developing, in this clip we see that the participants are

Not deterred by the closed door

Working as a group

Protecting their identities

Inflicting material costs to the institution via property destruction

Getting away at the end