Mercury is rather uncomfortable in Pisces. Our quick-witted planet of thought, communication, technology, and expression likes things to be oh so precise and efficient. The symbol for Pisces is two fish swimming in opposite directions, and Mercury finds this frustrating and debilitating.
In Taurus, instead of having his nose in books (which is one of his favorite things), Mercury is more inclined to channel and receive messages from the divine through touch, sight, smell, or otherwise through the senses. He has to slow down in order to do this, which goes against his grain….at first. Once Mercury gets to the 3rd decan of Taurus, he’s got this more earthy thing down.