Not to be confused with the high-jinx of transiting Mercury retrograde, its progressed retrograde periods only happen once in a lifetime. They last a couple of decades. During that time, your memories both of this lifetime and prior ones are undergoing a transformation. You are in essence re-writing your personal history, turning innocent delusion into true wisdom. And when Mercury goes Direct, stand back: if you got the retrograde years right, people are lining up to buy your book!