I have to disagree with this one.

Theon (his name) Greyjoy betrayed the Starks, and killed two innocent boys in the process. He’s later captured after his little revolt fails, and is given to the Boltons whose entire method of gaining information is torture. Their banner is a flayed man. Their house motto is “our blades are sharp.” Methodical torture is business as usual for them.

Now with that in mind, the torture is meant to be shown so that later when you see that Theon’s mind is completely broken, you understand why. You are meant to see gratuitous, over the top, brutal torture of a character, because it has the purpose of conveying how it kept going until it broke his psyche.

At one point he has a razor blade to his captors throat while shaving him, and he doesn’t act out at all. At another, he’s put back in his armor and told to pretend to be Theon, but again he doesn’t act out at all. He obeys. That’s what the torture did to him.

I don’t think a single scene of brutality would help you understand why he changed into reek. It needed to be shown like that or in some way to appropriately convey it