Remember, the goal is to keep you in the store as long as possible, and to make you pass as many shelves as possible. You can't buy the new nacho cheese flavored Hamburger Helper if you don't know it exists.
Why It Works:
We know that rotational patterns like this are common in herd animals, like elephants, but nobody is quite sure why humans do it. Studies have shown that British, Australian or Japanese shoppers tend to go the opposite way (clockwise) through the store, so some have speculated that it's based on the side of the road you're most used to driving on. If you drive on the right, you head right and follow the wall around.
But whatever causes the impulse, it's really strong. A store in Philadelphia wanted shoppers entering their store on the left, and to move clockwise. They forced customers to enter using the left entrance, only to see them immediately head to the right once inside. The managers then put down several pallets of goods in the way, thinking shoppers would just shrug and turn left and continue shopping. They were wrong. Customers struggled by the blockade to the right, shoving their carts through, demanding to move in a counterclockwise fashion, "as determined as salmon swimming upstream."