Allegedly a fundamental rule of feng shui, in which a bed or seat is situated diagonally farthest away from the entrance to a room and there is support behind the position in the form of a wall.
Interestingly, because western languages are written left to right we tend to experience life, theater, movies, and television the same way. This is because physical movement and memory have associated emotional values, and perhaps a metaphorical link between motion and memory.
If you are right-handed you associate positive emotions with rightward directions, and negative ones with leftward directions. Left-handed people associate positive emotions with leftward directions.
Whatever your handedness westerners commonly associate up and forward with positive feelings and associate down and back with negative ones.
A position of power or command is said to occur when you stand at the entrance to a room and a bed or desk is to your right. In stagecraft this seating arrangement typically signifies royalty. Late-night television hosts are typically filmed with their seats to the right. Anyone appearing to the left is therefore in a subservient, and less positive, position.