In any military society, the left is the shield side (the right holds the sword). If a commander were to be ambushed or attacked while not actively carrying a weapon or shield, the subordinate would be in the way: the attacker would take so long to remove them that the commander could then retrieve their own weapon and defend themselves.
It possibly originates from the idea that for most (right handed) people, this is the side where they are easiest to attack, so the person to the left can serve them by defending their left.
The left femur is superior to the left knee.
The right hypochondriac region is superior to the right lumbar region.
The right hemisphere is superior at creativity and spacial awareness.
Left ventricle
Left Kidney
The Right lung has 3 lobes (superior, inferior & middle) while the left lung has 2 lobes (superior & inferior).
superior vena cava
The Right lung has 3 lobes (superior, inferior & middle) while the left lung has 2 lobes (superior & inferior).
Atria (left and right)
Left
On the Left.