It takes a bit of doing, but try this mental task. Imagine a right hand glove with the thumb towards you. Then imagine every point moving so that it gets flatter and flatter until it is completely flat. Then - impossible in the real world - let them keep moving until the thumb is as far behind the fingers than it was in front. You will find that this front-to-back change has also changed it from a right-hand to a left-hand glove