Defense in Bridge is nothing but partnership rapport. A good steady partnership has all the ingredients for executing a good defense at Bridge specially in those deals where a farsighted defense is not so obvious. Of course when partners are not of equal caliber, things often fall apart and the defense can go haywire because the weaker partner at times cannot pick the right line of defense under pressure. However, with both partners of equally high caliber, the signaling at defense is like breathing with no visible effort. But even here, as human beings prone to error, partner at times needs a life line to save himself from sinking. It is in such circumstances that other partner must oblige and do all that it takes to make life easy for his partner. In Bridge your signalling for shift of suits and discards can have a very telling effect on your partner's play at defense. You see at times what you can visualize may be a double dummy play in defense but the same may not be so clearly visible to your partner. It is no consolation to cry over spilled milk. A lot of post play analysis telling partner innumerable ways of preventing that error made in defense is no good once the damage done is an irreversible one. Would it not have been better to do that which could stop partner from making the error in the first place and avoid that losing line at defense?
A simple little illustration can supplement the above. For example, say partner leads 9S against declarer's heart contract and you sit over dummy's Axx, holding Jxxx. If dummy plays low, you should do likewise. Putting up the jack in third seat does not help at all since you know the 9S from partner marks declarer with all honours inclusive of the 10S. You see if you insert the J and declarer takes the K, partner might be misled to believe that you can hold the QS and hence later on gaining an entry continue the suit in vain.
Let us now take our illustration in defense at Bridge for today as under.
Sitting east, you see partner's opening lead of 7C hit the table. When you play the QC declarer takes it with AC and plays a low diamond to partner's 10D with dummy playing the Q to the AD from you as east. Your 10C is next allowed to win. Recognizing partner's 10D as a singleton, you go for the next diamond which partners ruffs with 4S. Now comes the KC from partner. The critical point of defense has come. What is your discard on partner's good KC?
Any average defender would without giving much thought to the partner's expected problem ahead, throw an irrelevant Heart expecting the contract to go down in any case after the defenders having already taken 3 tricks are looking for 2 more in majors with partner surely holding a trick in spades and also holding the likely AH as apparent from the bidding wherein south passed 2S showing minimum hand and has already come up with 8 points having shown the AC plus KJ of diamond's. At most he can hold either AS or KJS to make up his opening hand.
The point is what should be east's thoughtful defense to make sure that partner does not slip in his tally of tricks to defeat the contract? Let us analyze what east knew at that point. He knew declarer had 2 Clubs and 5 diamonds along with his presumed 5 spades as he had rebid spades and therefore, a singleton heart holding. Here lay east's great foresight. He feared that if declarer led his singleton heart next, partner in all innocence might just duck to give what in partner's mind could be a hard guess for the declarer to play from the KJ holding in dummy in diamonds. Naturally the declarer if given the chance would go for the KH. That would be catastrophic for the defense giving the declarer his contract by way of 4 trumps, 1 club, 1 heart and 2 diamonds plus a diamond ruff in dummy. The Defenders had their cake all cut and ready to eat having taking 3 tricks plus 2 major aces to follow to down the contract of 3S.
So east made the most thoughtful discard to ensure that his partner cashes his heart ace immediately. He therefore, discarded his queen of hearts! West now had no hesitation to cash his heart ace at once and his AS was the setting trick thanks to his partner's judicious discard in defense!

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 North          East
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 Q 10 9           62
 K J 72         Q984
    Q 9        A8752
8 6 5 4          Q10
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S       W      N       E
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1S      P     2S       P
P      3C      P       P
3S              ALL PASS
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