(idiomatic expression) a short way of saying whatever comes easily also leaves easily; people often say this in reference to money.

what goes up must come down: (old saying) this phrase is often used to express the idea that good situations eventually turn bad.

A: "Why do you look so sad?"
B: "That guy I met in the cafe last month just dumped me for a girl with big breasts."
A: "I guess it's easy come, easy go, right? "
B: " Yeah, I guess so."
A: "You know, life isn't always happy. What goes up must come down."
B: "Why do you always speak using cliches? Can't you come up with anything original to say? You are not helping me feel better."

摘自中国日报网站(J-04)