It’s believed that left hands are impure and wrong. We never shake hands with left hands.
That’s why the other is called “right hand”.
In Japan, most people wear prayer beads on their left wrists to block those bad spirits from coming into their bodies.
Why are left hands bad?
One possible reason is related to the position of our heart.
Using left hand too hard can be a burden to the heart so we avoid using left hands too often.
It’s said that those sumo wrestlers try not to get strong impact on the left chests. I heard those electrical engineers use right hands not left hands to touch electric tools to avoid direct electric shock on the heart.