Maybe every time you wanted something for yourself, you heard the same thing.
“Don’t be so selfish.”
So you became a giver. Now you keep attracting people who only take, exactly the kind of people you can't stand.
Until the day you've had enough, and you swing to the other extreme. Suddenly you overreact, you put up walls, and even a small favor feels like someone taking advantage of you.
Then the guilt comes, and you go back to giving.