Literally, what is good for a female goose is equally good for a male goose (gander); or, what is good for a woman should be equally as good for a man.
If something is good for one person, it should be equally as good for another person.
https://www.yourdictionary.com/what-s-good-for-the-goose-is-good-for-the-gander
本意是男女一样，但可以延申
