"Don't count your chickens before they hatch."
I've heard that one all my life. Here's what the Cambridge Dictionary has to say about this old adage; "you should not make plans that depend on something good happening before you know that it has actually happened"
This is a terrible message for any of us, especially our youth, it implies that any good thing happening is a matter of some kind of chance or luck; that life is some kind of lottery where good things happen randomly only to the "lucky" ones.