@Chiiyuu "No one would act like this in real life." Unfortunately for you, you don't know how deep and complex the human mind is, especially given their circumstances.
The common trend for these kind of characters is that they lived in a life of wish-fulfillment, fangirling over their favorite game and dreaming how it'd be like to really be there. Once you give someone like that power, in a position where she can manipulate the future as she wishes in her favorite world, a person like this WILL come out once that world starts defying their expectations. I mean, to them, the world is their favorite game brought to life, so they know all the rules and the ins and outs. That's why to them the world should bend over for them, and will break down their psyche and lose rationality and then sanity once things don't awry when they do everything they know through their understanding of the world as a game is done perfectly, and yet shit happens to them.
As what Robert Green Ingersoll said ABOUT Abraham Lincoln (which is misquoted to be from Abraham Lincoln himself):
"Nearly all men can stand adversity, but if you want to test a man's character, give him power." And these kinds of characters, including the lot of isekai characters really, fit the bill.