Definition
This idiom is used to caution someone about being careful with their spending, as money is a limited resource and not easily obtained.
"I want to buy that designer jacket." "You'd better think it over; money doesn't grow on trees."
"Can we have a fancy dinner tonight?" "Of course not, money doesn't grow on trees, we need to be economical."
"Dad, I need a new phone." "Okay, but you must understand, money doesn't grow on trees."