The phrase "on the other hand" is used to present an alternative perspective, consideration, or argument in a discussion or comparison. It indicates that there is a different viewpoint or an opposite side to what has just been mentioned.
The phrase "on the other hand" comes from the physical act of using one hand to represent one side of an argument or situation, and the other hand to represent the opposing side. The use of "hand" in this phrase dates back to the physical representation of alternatives and contrasts.