it ain't over till/until it's over

The final outcome cannot be assumed or determined until a given situation, event, etc., is completely finished. Usually used in reference to organized competitions, such as sporting events, political elections, and the like. A: "We're down by six points with only two minutes remaining. There's no way we can win now!" B: "Hey, it ain't over till it's over!" It's not looking likely that the senator will be elected to another term, but it ain't over until it's over. Why are you being so pessimistic? Have some faith—it ain't over till it's over!