The time to ignore the Boston rule
George Ade, a humorist and playwright who died in 1944, said, "To insure peace of mind, ignore the rules and regulations." I once mentioned the key rule that when one leads a low card from a long unbid suit, it should contain at least one honor. With no honor, lead an unnecessarily high card. There is an acronym that is approximately correct: BoSToN: Bottom of Something, Top of Nothing.
However, as is usually the case in bridge, there is a critical exception to the rule. When you lead the suit partner bid, and you did not raise his suit, it is more important to give length information than strength information. You lead high from shortness and low from length.
Today's deal highlights why this is so important. Look at the West hand. What should he lead after his partner opens one heart, and South jumps to four spades?
South should not go more slowly in the bidding. If partner has only the diamond ace, the contract will be laydown. Also, it is highly unlikely that North-South have a slam, given East's opening bid and North's initial pass. West leads the heart two. East wins the first two tricks in hearts. Knowing that declarer is now out of hearts, East shifts to a low diamond, and two tricks in that suit defeat the contract. Note that if West leads the eight of hearts, East will think it is from a doubleton and try to cash a third heart trick, which lets the contract make with an overtrick. Declarer draws trumps and runs the clubs, aided by the appearance of the jack and queen.