Question

Oh, my goodness!
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Why do we have to use 'goodness' here?
What meaning does 'goodness' have here?
Writeacher
It's just an expression, usually used when one is surprised! I think it's a way to get around using "God" in a casual expression like this.

Other tutors may have more ideas about this!
Ms. Sue
I agree with Writeacher. I'm sure you have expressions in Korean that express surprise.