You are West, declarer in 3NT, against which North leads the Q♥. What is your best line of play? Counting tricks, you see two hearts, two diamonds and four clubs; one more diamond can certainly be developed to make your ninth trick.
But the danger is that, if you duck and allow north to take the first heart trick (as you did yesterday), he may switch to a spade, find South with length and the ♠AQ, and you will go down before you get started.
Win the first heart and finesse diamonds into South’s hand. Even if he wins this trick, he can do no harm, as a spade switch from his side of the table will now even give you an overtrick.
if he simply returns his partner’s lead you have your nine tricks established.