Here are two declarer play problems:     (1)
 K Q 10 7 2 J 4 3 7 4 A Q 3 A J 4 3 Q 7 6 2 A Q 2 K 7
Contract: 4 by West Opening Lead: J  (Note: Trumps are not 4-0). (2)
 A Q 3 A Q 4 2 J 6 5 4 A 6 K J 4 K 7 5 A 9 2 K Q J 3
Contract: 6NT by West Opening lead: 10

Solutions

# ⇓

(1)
 K Q 10 7 2 J 4 3 7 4 A Q 3 A J 4 3 Q 7 6 2 A Q 2 K 7
Contract: 4 by West Opening Lead: J  (Note: Trumps are not 4-0). (1) 4 is no worse than an even money proposition, depending on the location of the K. Is there anything better? You might try leading hearts toward the jack twice. If South holds the ace-king you might build a heart discard to pitch a diamond. Not too likely and this might easily lead to three heart losers and a diamond loser. The good news to brighten your Sunday is that 4 cannot be defeated if you play it correctly. Win the K, draw trumps, play the A Q to discard the 2 from dummy, then play A, Q, giving up on the 50-50 finesse. Whoever wins theK will have to play a club or diamond, allowing you to discard a heart while ruffing in dummy, or will instead break the heart suit, in which case you will play second hand low and lose only two tricks in the suit. (2)
 A Q 3 A Q 4 2 J 6 5 4 A 6 K J 4 K 7 5 A 9 2 K Q J 3