It is just like English sayings and phrases, there are Japanese sayings and phrases as well. It is called [kotowaza ことわざ].
魚心あれば水心I Uo gokoro areba mizu gokoro
Uo – fish
Mizu – water
Kokoro/gokoro – heart
If you have a fish heart, you have a water heart
If a fish wishes that he wants to live in water, then water responses to it and try to become a comfortable nice water.
If you try to get along with other person then other person also try to get along with you.
How to use it
Watashi wa chiisai itoko no omamori yaku da. sono aida ni, oba san ha kamono o suru. Uo gokoro areba mizu gokoro to iuga, oba san ha otoshidama o oomeni kureta.
I am taking care of my little cousin. In a meantime, my auntie go to shopping. It has been said that if you have a fish heart, you have a water heart. My auntie gave me more money than I thought.
I have experienced many times that when I treat nice and respect and appreciate then other person also do the same to me. If we disrespect other then other also disrespect you. What goes around comes around.