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This dream, I think, may be the contrast between two kinds of life.
Your aunt gave you a cheongsam. It's beautiful. You chose a beautiful one. Represents a good life.
Your mother gave me a big coat, which is heavy, indicating that life is hard and heavy.
I think your aunt's life might be better. You may want to live like your aunt (beautiful and happy), not like your mother (heavy).
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Interpretation of dreams is very complicated. Beginners can interpret dreams indiscriminately and play while watching.