Don't count your chickens before they hatch

Hello. My sister used to ask you questions when she was in 4th grade. Now I'm in 4th grade and I have the same teacher. She asked us where the phrase - Don't count your chickens before they hatch came from, but I want to know what it means! Thank you very much. Will from Mrs. Morrissey's class

It means don't rely on something until you are sure of it. Don't think that because you have 12 eggs, you are going to get 12 chicks!

DFG