Mercury is a very small, but dense, planet that orbits the Sun about every 88 days and turns retrograde three or four times per year. All of the major planets, except the Sun and Moon, turn retrograde, but none turn retrograde as often as Mercury. That’s why you hear us astrologers chirping about Mercury’s retrograde so much.
When a planet turns retrograde either we (the Earth) are passing it, or it is passing us on our solar race track. And, just like when you pass a car on the highway, for a short period of time, the planet (auto) appears to be moving backwards. So, when a planet is in retrograde, it is closer to the Earth than it is in other parts of it’s orbit. Because the planet is so close to us, it’s gravitational pull will have a stronger influence on our personalities.