Although he was plucked from his home after the Greyjoy Rebellion and made to serve as a ward to Ned Stark in Winterfell, it really wasn’t that bad. Theon befriended the Stark boys and was basically raised as a highborn lord, where he received an education, fighting skills, and more.
But Theon never could quite figure out where his loyalties belonged.
As a result, he turned on the Starks and captured Winterfell during a sneak attack. Except he quickly regretted it when he had to take action against the same people who helped raise him. His short stint as ruler of Winterfell was ill advised and eventually led to his capture by Ramsay Snow, subsequent torture (including castration), and years of living like an animal.
Long story short, when you have a good thing don’t screw it up by going against the people giving you every advantage. Lest you become Reek.