For me it was learning the anatomical position used as a reference in medicine. It places the person standing in front of you, with their head and palms facing you. Their right is in your left side, and their left is on your right side. I got so used to referring to a patient’s left or right that I have to mentally reverse that to speak of my own.
Up and down are a lot more obvious and straight forward. In an anatomical position, up and down don’t change.
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