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[ ] gifts, we all experience positive feelings. According to the latest research, when [ ] someone presents, we feel the same or even bigger emotions. [ ] something for ourselves, we can't get the same pleasure each time. [ ] to be unhappy with what we have, we want more and more. This happens because our brain can't get satisfaction from the same [ ] actions. [ ] a present, on the opposite, is every time something new. Besides, [ ] social creatures, we tend to share other humans' feelings, which is called empathy. [ ] a happy face of the receiver, we cannot but feel the same pleasure ourselves. [ ] joy is a double joy.