kindness begets kindness; you scratch my back and I'll scratch yours
Proverb meaning that if you show goodwill to others, they will respond in kind. The literal image is that if a fish is kind to the water, the water will be kind to the fish.
As the saying goes, kindness begets kindness; if you are kind to others, they will be kind to you in return.
A traditional Japanese proverb. The literal meaning is 'if a fish has a heart for the water, the water has a heart for the fish,' expressing mutual goodwill.