North–South have 27 combined high-card points, so East, the opener, surely holds the relevant missing values, namely, the ♦ K and the ♣A. If you win the heart lead in hand and take the losing diamond finesse, you’ll have only eight tricks (two spades, two hearts and four diamonds).
If you attack clubs first, however, you can get four tricks in the suit. The major-suit ace-kings and the ♦A will bring your total to nine.
It would be a mistake, however, to play the ♣K at trick two. If East has the singleton ace, West will have another stopper in clubs, and the contract will fail. Best is to play a low club from dummy at trick two toward the queen. If East goes up with the ace, you have nine tricks. If the ♣Q wins, you can play on diamonds to come to nine tricks. The opening lead, therefore, should be won in dummy. The full deal: