The opponent needs a gentle nudge
Ring Lardner, a sports columnist and short-story writer known for his satirical pen, wrote, “A good many young writers make the mistake of enclosing a stamped, self-addressed envelope, big enough for the manuscript to come back in. This is too much of a temptation to the editor.”
In this deal, declarer must tempt East into error. South is in four spades. West cashes the top three hearts, everyone following, then shifts to the club seven. How should South continue? Some pairs lead the queen from ace-king-queen. This has the advantage that when an ace is led at trick one, third hand knows his partner has only the ace and king. South was right to bid game with such a good fit and a side-suit singleton.
Declarer must draw trumps safely. If they are 2-1, there will be no problems. But just in case East has all three, South should cross to the board with a diamond and lead specifically the spade jack, tempting East to cover with the queen. Here, if he does, declarer makes his contract, finessing East out of his spade 10. Or East may think for some time, giving the game away. But if East plays low smoothly, South will win with his ace, not risking going down when West has a singleton or doubleton queen.
If declarer leads an unsupported honor from the dummy and you have that card surrounded (with at least one more low card), it is (almost always) wrong to cover.