Don't assume a positive outcome will happen until you know for sure. The full saying is "<strong>don't count your chickens </strong>before they hatch." This means that if you just count your eggs and assume there will be a chicken in every egg, you could be disappointed to learn that some eggs did not contain a chicken.

For Example:

a friend could say, “I’m really excited for my big Christmas bonus this year.” But if receiving the bonus was not a foregone conclusion, another friend could respond, “don’t count your chickens before they hatch!”