Source: http://lidororen.blogspot.com.ar
Dealer West. East-West Vul. Difficulty level: Hard.
You are playing 4
. West lead the 
4. You tried the Q, but East covered with the K. This one is a real challenge! Let’s see if you make it!
- Where is the J?
- Where is the
A? - Where is the K?
- Where is the Q?
- Where is the K?
- Where is the
Q? - Do you win the trick? If so, what will you play next? If not, why not?
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
⇓
Where is the J?
With West. West lead a low card which promises an honor. Since the K turned up with East, the J must be with West.
Where is the A?
With West. First, if East has the A, it means that West doesn’t have 12 points for his opening or his 3 bid, vul against not. But even if he chose to open light due to his 6-carder, he would have had the KQ, and no doubt he would prefer to lead the K, rather than underlead a low spade from his J.
Where is the K?
With East. If West would have had the AK, he would surly lead a top club.
Where is the Q?
With West. If East has K and KQ, then West would have only 10 points which doesn’t justify his opening nor his 3 bid.
Where is the K?
With West. East has both black kings, so West has all the rest.
Where is the Q?
With West.
Do you win the trick? If so, what will you play next? If not, why not?
Win the A and continue diamond at trick 2, finessing to the 10 when West plays low. Cash the A, and continue with a heart to the A (you might drop the K). After both opponents followed low to the A, continue with the K, throwing a spade from dummy. Now ruff your spade loser in dummy. You will lose in total only one heart and 2 clubs. If you play the A at trick 2, you have no entry later on to the K. You have 4 immediate losers. You must therefore throw the spade before losing the lead.
Things to remember:
Timing is a valuable term in playing the hand and in defense. Timing means: When to play each particular suit, When to win a trick, when to hold up, how many entries are needed etc. In other words Timing is the order you play the cards. Also in the given hand Timing is highly important. Any other way to play it will make the contract fail: You must win the lead, finesse diamonds at trick 2, cash A, and keep the A as an entry to the last diamond for a spade discard.
If you play a suit contract and you are missing the Ace and the King in a side suit, and the opening lead was another suit, away from an honor, that means that the leader doesn’t have the AK. If you miss the AKQ in the same suit, and the opponent on lead has most of the missing points, it’s likely he has the AQ.
Try to avoid underleading a suit headed by the J (prefer leading low from Qxxx rather than Jxxx).