It is just like English sayings and phrases, there are Japanese sayings and phrases as well. It is called [kotowaza ことわざ].

Today’s kotowaza

鬼に金棒　Oni ni Kanabo

Oni – a deman

Kanabo – a metal rod

make one even stronger

Its origin

If a stone demon gets a metal rod it make him even stronger!

Its meaning

Person who is powerful already become even much stronger by adding much power.

An example

My brother joins the strongest baseball team in the city. What’s more, a famous coach will be coming next week, well, it is Oni ni kanabo!

arigato