You are P1 and leading by 1 point. There are 2 provinces left, but no duchies or prizes, and there are no victory cards in the supply. You know your opponent has no +buy in his deck, and has enough in hand to buy a province. You don't have enough to buy a province. You know your opponent reads dominionstrategy.com and so knows about PPR, and you have a late stage Big Money deck (or something else with high hand-to-hand variability). Your opponent's deck can generate $8 consistently.
If you reveal a province, that increases the chance that your opponent thinks you can't buy a province this turn, in which case he will buy a province, and you will very likely lose (you'll have to buy an estate, which will leave you down 4 points, and your opponent's deck is more likely to buy the last province). If you don't reveal the province, your opponent may follow PPR and buy an estate, figuring that if he buys the province, you may win the game, but if he buys an estate, he can play for a draw.