Why is it considered a bad time to do business when mercury is in retrograde? How did this originate?

Mercury is the planet of Communication. When it is going retrograde, or backwards, all things communication-wise can get pretty messed up. Important business calls get dropped, flights get missed or delayed, interpretations in conversations get mistaken, etc. As you can imagine, not a good thing for an area so heavily reliant on communication!

Planets that normally appear to move from Aries towards Taurus, at times, appear to move backwards, from Pisces towards Aquarius and so on. The Sun and Moon are immune to this apparent backward motion.

The reason for this apparent retrograde movement of planets varies. For the inferior planets, Mercury and Venus, when they are between earth and the Sun, they appear to move direct; however, when they are on the other side of the sun (Sun is between the planet and earth), they appear retrograde.

Many views exist on the astrological implications of such apparently retrograde phases of planetary motion. Most astrologers agree that at least subtly different effects are produced by the same planet when it is in direct in contrast to retrograde motion. Retrograde Mercury is anecdotally associated with communication breakdowns, more computer troubles, etc., and causes much anguish in certain circles. Some astrologers tend to put too much emphasis on the retrogression phenomenon.

Some astrologers consider a retrograde planet as a 'blocked' or deficient responder! By that token, one with a retrograde Mercury would not find logical thinking very easy or even something within one's capability. The retrograde planet appears to move backward in the zodiac due to our geocentric viewpoint and it is easy to fall into the trap and consider the apparent backward motion as something 'negative' because of its symbolic parallelism with the connotation of the term 'backward'! Perhaps during the periods and transits of retrograde planets, one needs to undergo a "paradigm shift", in other words, to embark on an alternate approach, using a very different viewpoint of looking at the same thing.

Mercury was also the Greek's god of commerce, then when he was moving backwards was a bad sign.... a recession !

It originated in exactly the same way all other astrological predictions originated: somebody made up some $hit.

that is an astrology question.

astrology is not science.

there is no correlation between the planets and buisness. unless you are working at NASA