My sister must have been using loaded dice. Every time we played Monopoly, she would waltz around the board, landing on her properties or bonus spaces. Meanwhile I would wind up in jail if I was lucky. I believed if we had the same amount of luck, I would have beaten her. We had to stop playing when I threw the dice in anger and one of them disappeared forever. 

The luck of the dice is eliminated in duplicate bridge. You get the same hand as everyone in your seat. The finesse that's offside for you is offside for everyone else too. That bad split is plaguing every declarer. 

Here's a bad habit for a duplicate declarer: trying to make your contract. When playing a home game or IMPs (and, frequently, in lessons) we try to make our contract. But when playing matchpoints, making your contract shouldn't be your goal. Your goal should be to take more tricks than other declarers. Your score (the percentage at the end of the game) is based how other players did with your cards (as opposed to how many points you score total). A better score is better, whether it's game making vs down one or the extra ten points for being in notrump instead of a suit. Take a look at this matchpoint table: 

Table	Contract	Result	Score	Matchpoints for NS
1	4-S	=	420	4
2	1NT-S	=	90	3
3	3NT-S	-1	-50	2
4	3NT-S	-2	-100	.5
5	3NT-S	-2	-100	.5

There are four matchpoints up for grabs for each NS pair (they can do better, worse, or the same as the other pairs). The NS pair at table 1 earned all 4 matchpoints for +420. That score beat each other NS pair's result. It doesn't matter that they were 330 points better than table 2 and 470 points better than table 3. Pair 2 got 3 matchpoints for making 1NT. Pair 3 got 2 matchpoints out of 4 (50%) for going down 1. Not bad! Going down two is a big loser here, yielding .5/4 matchpoints or 12.5%. 

Matchpoint strategy becomes really important when you're deciding whether to be really aggressive in making your contract or not. Take a look at this deal: 

Auction: 

Lead: 5

The first two tricks: 5, 4, K, 8. 9, J, 2, 3. You win the second trick in your hand. What's your plan? 

We can count five diamond tricks, one spade trick, and one club trick for seven total. Where can we get more? Hearts could provide three tricks once we knock out the ace. Clubs can provide two more tricks if East has both the K and J. 

Before we decide which path to take, we need to assess the spade situation. How are spades splitting? 

West has 5 spades and East has three. We can tell because West started with the fourth-best 5, followed by the 2 (the only remaining card lower than the 5). East played the K and then a high card which looks like it is high from two remaining. All of that is consistent. It also means, that if either opponent wins a trick, they can take three more spade tricks (in addition to the one that they have already taken). 

Should you play on hearts or clubs? 

Down one, here we come! We're in an absolutely normal 3NT. West led fourth best. You expect all the other tables to be doing the same thing. The odds of East holding both the J and K are 25%. That means that you'll succeed a quarter of the time, but fail 75% of the time. In matchpoints, that's a bad proposition. It's much better to take your medicine and play hearts. 

Full deal:

Vul:None Dlr: S	43  KJ6  AQ1052  987
A10652 972  97  K54		K97 A85  864  J632
	QJ8  Q1043  KJ3  AQ10

Note that West made a good play of ducking the second spade (ensuring communication). It's good technique. If you tried the club finesse, you'll go down two rather than down one. At IMPS, you'd risk the finesse for the reward of making a game. The same is true at rubber bridge, where down one or two isn't a big deal, but that difference is key at matchpoints. Fair is fair.