@NaciremaMi
Some stuff I'd like to add, especially since what the other's said isn't strictly accurate:
Our MC knows this game very well, and in particular there's two things he's extremely concerned about:
1: The Harold in the game is basically a recurring miniboss and the most hated character in the game by far, because of all the heinous stuff he does to various characters.
This means that one branch of death flags comes from getting lynched by the main party or others, especially tricky to avoid as his mouth uncontrollably has no filter and on rare occasions he loses control of his body / actions if a scenario crops up that's very similar to any of the cutscenes in the game that involve him - this already happened twice in the first few chapters.
So if he has to worry about getting killed by the main party and generally getting killed by an angry mob, then why doesn't he just go off into the mountains and live as a hermit or something? About that...
2: There's a threat to the world coming that will completely & utterly destroy it in about 11-ish years from the start of the novel.
The end boss is extremely intelligent and cunning, so he can't simply change one thing and completely avoid it happening as they would simply change their plans accordingly. He also can't go beat the end boss by himself as it has to be the hero and his party that does it, the plot of the game is a close call prevention of doomsday and the only way he knows how to go about it is if events closely follow the plot of the original game, and Harold himself plays a pivotal role in it in multiple encounters, even if it's just the experience for fighting him so the hero's party is strong enough to beat the final boss.
So, he's trying to have things follow the original plot as closely as he can, but in a way that doesn't get him actually killed at the end of it all. He's also trying to save lives wherever he can, he doesn't want to sit around and watch people lose their lives if possible and wants to evacuate cities if an impending disaster is coming and stuff like that.