a different kettle of fish
1
an issue or subject that is not in any way connected to what one was talking about
The idiom "a different kettle of fish" is believed to have originated in the 18th century. It is thought to have come from the custom of preparing fish in a large pot, or kettle. If the fish were different types of fish, the cooking process would be different for each type. This led to this phrase being used to describe any situation that was different from another.
- Managing a large team of employees is a different kettle of fish from managing a small team.
- Trying to resolve a conflict between two people is a completely different kettle of fish than trying to resolve a conflict between two countries.
- Starting a new business is another kettle of fish from running an established business.
- Learning to drive a stick shift is an entirely different kettle of fish from learning to drive an automatic transmission.
- Raising a teenager is a different kettle of fish from raising a young child.