It has been said that one peek is worth two finesses, but to an attentive declarer, an opposing bid can sometimes be worth even more.
Consider this case where South wound up in four hearts after West had opened the bidding with one club. West started with the K-A-J of clubs, declarer ruffing the third round.
South could count three certain losers — a diamond as well as the two clubs already lost — plus a potential loser in spades, where a finesse was available. However, since West was highly likely to hold the king of spades as part of his opening bid, the finesse did not figure to succeed. This conclusion was reinforced by the fact that East — who did not answer his partner's one-club opening — turned up with the queen of clubs on the second round of the suit. An alternative plan was needed, and South came up with the answer.
After ruffing the third club, declarer reeled off four rounds of trump and cashed the ace of diamonds to produce this position:
When South now played his last heart, West could not afford to discard a spade or the nine of clubs, so he let go of a diamond. Declarer thereupon crossed to the king of diamonds and led the eight of clubs, on which he deposited his last diamond.
West won with the nine but was forced to lead from the K-J of spades into South's A-Q, and declarer's spade loser simply vanished.