Again a diamond lead is effective for a quite different reason.

A diamond lead would have succeeded at this point, but South had something else in mind.

The position was this: South had no way to know that a low diamond lead would have a happy result, and led a heart.

A diamond lead was the only one to beat the contract.

East won, and was able to enter his partner's hand with a diamond lead.

Unfortunately West did not know that a diamond lead was necessary.

South had better information and knew that East was hoping for a diamond lead.

A diamond lead would have been effective, but South had a different plan.

The diamond lead was won by South who led the heart jack.

When East won the next diamond lead, he shifted to a low heart, but it was too late.