Truth of the matter is, you need to count both winners and losers in all contracts. But lets start by looking at losers, because doing so often leads to eye opening results.
Example 1. You've arrived at a pushing 4♠ contract, lead is the ♥K
Lets count losers.
2 trump losers, 2 heart losers, no diamond losers, 1 club loser. That totals 5 losers. So lets say you draw a trump now, opponents could just cash out their winners and take you two off. So what is the solution to the problem? Please think before reading on.
The question always becomes "How can I get rid of some of my losers". Specifically in this case, how can I get rid of two losers at least (because you are only allowed to lose 3 tricks for this contract).
Do you see how? You could cash your diamonds, which would allow you to pitch one loser. But that would still leave you with four losers.
The solution is to take a diamond finesse. Hope for the best, and if that works, you get two pitches on the Ace and King of diamonds, which you can throw two losing hearts on. If the diamond finesse loses, you will likely go three off, but if it wins, you will likely make the contract.
As a final point, its important to see that you need to take the diamond finesse urgently, before drawing trumps. If you drew trumps too early, you would lose the lead. The opponents would seize that, and cash their heart tricks, before you can throw them on your diamond winners.
Lets continue, example 2. Playing in 4♠ you get the ♥Q lead.
As always, we do the boring but incredibly valuable task of counting losers. 1 trump loser, 1 heart, 1 diamond and 1 club.
The thinking should go like this: "nothing to do about the Ace of trumps, that's a certain loser. Club loser looks certain also, as does the diamond. If I play diamonds early though, I can pitch a heart on the second diamond".
There is a further pattern to these two hands. If one hand has shortage opposite the other hands trick source (in both this example and the previous example diamonds were the trick source, opposite a shortage), its possible that you can throw losers from other suits on that trick source (since of course you won't be following suit, as you are short in that suit! Glance again at the diamond suit above if this isn't making sense to you.
So the solution is to play a diamond immediately. Win the heart, return, cash a diamond trick, pitching a heart, then start drawing trumps. Note that once again, you cannot afford to waste time drawing trumps before you have set up the diamond, or else the heart loser will be exposed before you can set up the diamond (After winning the Ace of trumps, they will return a heart).
Lots more to come on this topic, and lots of practice exercises to come.
A hand that found a blind spot in the semi finals of the US national team trials.
You are south in 4♥ on an uncontested auction. A trump was lead, 2 8 9 10. What next?
What you really want to do is draw trumps and make a flood of diamond tricks. It looks like you have lots of tricks, say 4 hearts, 6 diamonds, that's already 10, but then add in a spade as well. However, its important on this hand to realise that if trumps break 4-1, you will need to lose the lead. At such time, the opponents can cash two club tricks if dummy’s trumps are gone.
So, as much as you would like to draw trumps, you can’t, you have to start by anticipating losing the lead. A club at trick two is the only way to make the contract, setting up the ruff before drawing trumps.
Another way of looking at it, its normal to count losers. The difficult part in this hand, is to count losers that will be there IF you draw trumps. So if you draw trumps, you open yourself up to two club losers (which you might not foresee when you count losers at trick one).
It is fairly normal to ruff in dummy before drawing trumps so this play should definitely be on the radar.
At one table, in the semi finals of the trials, one player drew another trump and went down when they actually broke 4-1. Eventually losing 2 clubs, a trump and the ♠A.