William Hazlitt claimed that when great thoughts are reduced to practice, they become great acts. Well, this might be overstating matters in a field of endeavor like bridge, but the idea is reasonable.
On today's deal, North's two-heart cue-bid showed a good hand with at least three spades.
When West led the heart six, South assessed the situation. Why hadn't West led the heart king? Presumably because he didn't have both the king and queen. Mentally, South placed one of these cards in the East hand. Why hadn't West led a top diamond? Clearly because he didn't have the ace and king. South gave a diamond honor to East.
But East had passed over his partner's opening bid. The mist was clearing. If East had two red-suit honors, West had to have the black-suit queens.
South won the first trick with dummy's heart ace, played a spade to his ace and led a low spade, finessing dummy's nine when West followed with the six. After cashing the spade king, South paused again. West was known to have three spades and five hearts. One diamond and four clubs was surely impossible. With eight diamonds, East would have bid.
West had to have at most three clubs. Therefore, South played a club to his king and led the club two. When the queen appeared, South won with dummy's ace, played a club to his jack, returned to dummy with a trump and discarded a red-suit loser on dummy's club 10.