Nothing is over until it is truly over. Ask any sports fan and chances are, they will instantly recall a time their favorite team turned things around when it seemed impossible.
However, they probably also remember moments of painful regret after the same athletes lost what was supposed to be a sure win.
The subreddit r/PrematureCelebration is full of examples that prove one simple rule: keep going until the final whistle. It applies to other areas of life as well!