When this deal was played in a coaching session, only one declarer found the best line. Incidentally, he was also the only one who correctly evaluated his hand as an upgrade into the 18-19 range.
West led the spade queen, East correctly withholding the ace to keep a link to her hand. Declarer ducked that and won the next spade trick before cashing the diamond ace and king. When East produced the jack and 10, declarer placed the remaining 8-x with West and abandoned the suit for the moment. Declarer instead forged an entry to dummy by leading a club to the king. He then called for the heart queen. East fell from grace by covering that, a play that could hardly benefit the defense and here unblocked the suit for declarer, allowing him to score dummy’s fourth heart.
Say East plays small on the heart queen instead. Declarer finesses the heart 10 and then cashes the heart ace before getting out with the club jack. What can the defense do? If they win and play a club, declarer takes two tricks in dummy. Even if the defenders could cash spades ending in West, a diamond from that hand would just float around to declarer’s Q-7 tenace.
Other declarers either cashed their diamond tricks early, establishing a fifth winner for the defense, or led the club jack on the first round of the suit and never reached dummy for the heart finesse. (Note that declarer can recover after that start by cashing precisely two diamonds before playing another club.)