Always there will be slip between the cup and the lip. There may be coffee in the cup and the cup may be in your hand. But till you drink it you can't say that the coffee in the cup is yours. The same is the case in any game or examination or task. Till you complete and get the final result you can't say that you are the winner. The person in the second position may overtake the first person and the first person may become the second person. Many times we may be losing the game very narrowly. So it is true unless the declaration comes mentioning that you are the winner you can not celebrate.
Even in elections, some candidates may be losing by just small margins. Initial trends may be different but finally, the expected candidate may lose by minimum votes. That is why Election Commission will not declare the results till the margin is confirmed.