How to Harden Alistair on "Dragon Age: Origins"by Timothy Baron ; Updated September 22, 2017
"Dragon Age: Origins" is a fantasy, role-playing video game. Players control a team of adventures on their quest to rid their homeland of a monstrous horde. Each of the characters has his own personality, including Alistair -- the earnest, but effete, Templar. Throughout the game, his moral compunctions keep him from participating in some of the player's activities. He'll even leave the party if the player makes a choice he finds dishonorable. The player can mitigate this by hardening him. There's only one chance to do this and it isn't obvious when the chance occurs.
Proceed through the game until you've gathered an army from each of the factions. The next leg of the quest is to go to Denerim.
Visit your camp before entering Denerim. You'll find Alistair by the campfire. Speak with him and he'll mention that he has plans to visit his sister in the city. Agree to accompany him.
Enter Denerim and then go to Goldanna's House, which is at the edge of the marketplace by the blacksmith. When you enter, a cut-scene starts between Alistair and his sister. The conversation goes poorly, no matter what you say. After a minute of his sister's berating, Alistair leaves.
Follow Alistair out. Speak with him and he'll talk about how he doesn't understand his sister's attitude. Choose the option: "Everyone is out for themselves. You should learn that." This hardens Alistair and after that, he'll be an easier companion to please.
The only way to get an ending in which all the recruitable characters survive, including Loghain Mac Tir, is to harden Alistair. If Alistair isn't hardened, he'll insist that you kill Loghain on account of his betrayal at Ostagar, as it's the only honorable thing to do. A hardened Alistair will still be unhappy with your mercy, but he'll at least accept it.