Mercury is the fastest moving of the planets, the winged messenger of the Gods. In the horoscope, Mercury has to do with the changing influence of mental matters and our ability to focus rationally. This planet governs communications, exchange of information, education, and mental focus thru thoughts and words.
When Mercury is Retrograde, which occurs usually around three times a year for about 23 days at a time, then the mind becomes distracted for many, resulting in communication complications and disruptions, especially electronically, and mental fogginess. Computers and other smart machinery that do not believe in Mercury Retrograde still experience the effects of this transit. So do those who create and maintain these sensitive programs. It is a slight electromagnetic short-circuiting that occurs, disturbing the vibration. So the more sensitive the machinery or transmitter/receiver, the more the micro disruptions can occur. This can be applied to anything with a magnetic pulse, including the magnetite in our own brains that gives us a sense of direction and 3d Dimensional reality, such as time and space. Our perception of such things may be altered under Mercury Retrograde.
If you were born under Mercury Retrograde, as almost one out of 5 people were, then your mind tends to be otherworldly and often psychic, and your mental skills are unusual and often erratic, gifted in some way yet perhaps spacy in others. Mercury Retrograde born people often excel under Mercury Retrograde, but still have to deal with others who are challenged by this transit. They also have to deal with the 80% of the time when Mercury is not retrograde.