When opponents give you some information unwisely, make the most of it. Sitting North, my partner Paul Laliberte used an opponent’s unwise double to profit in an OK Bridge Internet game, with East dealing and no one vulnerable:

                          NORTH (Paul)
                         ♠️ K J 9 7 4
                         ♥️ A K 10
                         ♦️ 9
                         ♣️ K 6 4 3

WEST                                                EAST
♠️ 10                                                ♠️ Q 6 2
♥️ J 9 7 3 2                                      ♥️ 5 4
♦️ A K Q J 7 6                                ♦️ 10 8 5 4
♣️ J                                                  ♣️ A Q 9 7

                        SOUTH (Me)
                       ♠️ A 8 5 3
                       ♥️ Q 8 6
                       ♦️ 3 2
                       ♣️ 10 8 5 2

The bidding proceeded as follows:

East                  South              West             North
Pass                  Pass                 1♦️              1♠️
2♦️                   2♠️                 3♥️              3♠️
Pass                   Pass                4♦️              4♠️

DBL   All Pass

Opening lead: ♦️10

O.K., we were fortunate to land in game when East kept the auction open with 4♦️ and Paul took a chance on 4♠️. But the play was the thing.

With trumps presumably breaking 2-2, Paul would have cashed the ♠️A-K. But thanks to East’s double, he could place the ♠️Q there with at least three cards in the suit.

Therefore, once he ruffed the second diamond lead, Paul played the ♠️J. The idea was not only to trap the ♠️Q but ideally to pin the ♠️10. Sure enough, when East played low, the ♠️10 dropped. As a result Paul was able to pick up the trump suit and make the contract, losing only two clubs and a diamond.

The defenders could have set the contract by switching to a club at Trick Two. East would have cashed the ♣️Q or ♣️A, depending on whether North played the ♣️K, and proffered a second club for West to ruff. East will eventually win another club. That strategy is only obvious with “double dummy,” meaning with all four hands exposed. 

What’s more obvious is that East made a fatal mistake with that unwise double.