Dummy play has a fascination of its own. It excites and provides an opportunity for the declarer to think ahead using foresight and logic. Some plays are difficult and not too obvious at first like the problem below wherein NS land in a contract of 4S held on these cards as under:

========
North
========
J 10 9
7 6 3
K Q 4
A 10 8 3
========

=========
South
=========
A K Q 3 2
J 10 9
A 8 7 6
7
=========

The bidding opened with south bidding is, north 2C, south 2D, north 3S and south finally bidding 4S.
The opening lead is the AH, followed by the KH and QH. Already booked, the contract looks a bit dicey. For although 10 tricks can be counted with 5 spades, 3 diamonds, 1 club, and the possibility of diamond breaking 3-3 or with the opponent holding 2 trumps pitted also with 2 diamonds so that he is unable to prevent the 4th diamond ruff in dummy.
If you are in south's seat how would you play the hand? Well, there is a clear cut way to make 4S safe and secure. Can you see how? Yes by dummy reversible. After west cashed his 3 top hearts, he shifted to a club which declarer takes with AC in dummy. Now from dummy's view point if one cares to analyze, there are no losers any where else except in clubs. But then all 3 clubs can be ruffed in hand with the proper timing as follows. Ruff a club high with AS, crossed dummy with 9S to ruff another club high with the KS; back in dummy with 10S, you can ruff the last club with the last trump in your hand scoring the QS ruff to record 6 tricks. Now all that needs to be done is to get into dummy with the KD to knock out the opponents the last trump. The AK of diamonds bring the trick taking toll to 10 for the west east hands were as under.

====================
West            East
====================
8 7            6 5 4
A K Q 4        8 5 2
J 10 5 2         9 3
5 4 2      K Q J 9 6
====================

One next illustration focuses on sound reasoning in dummy play technique with WE landing in 4H on the following bidding holding the following cards.
The bidding went as under:

=========================
West                 East
=========================
3               A J 7 4 2
J 10 9 8 7 6          A Q
K 2            A 10 7 6 5
A 7 6 5                 J
=========================

==================
N     E     S    W
==================
3C    Dbl   P   4H
==================

The opening lead is the KC. As west in the declarer's seat, how do you plan your play in 4H?
On the face of it you have a trump loser and possibly a loser or two in clubs. The hands look not too difficult to execute for even with a trump lead, you would be able to ruff a club giving 2 clubs and a heart. So here's your chance to be able to ruff 2 clubs and just giving up a club and a heart to make 11 tricks. So grabbing your AC, you embark on your club ruffs don't you? Ruffing the 1st club with QH and then getting into the hand with KD to ruff the 2nd club with the AH thus loosing only a club and the king of hearts.
Easy isn't it? But oops - there is a twist in the tale. By the way did you ruff the club with the QH? Well if you did you had it coming on yourself for south over ruffs with KH and knocks out dummy's trump leaving you saddled with 3 club losers and the KH to make you go down in an otherwise ice cold contract. Now you see the correct line of play in retrospect but a bit too late to do anything about it.
All you have to do before for safety was to ruff the 1st club with the AH and not with QH to get back in diamonds to ruff the second club now with the QH. Whether south over ruffs or north does not matter, for now the tempo is with the declarer for a sure shot success. Those who do not pause to think logically and count one's safe tricks usually finish on the losing hand. In the actual play on the table, south ruff the 1st club with the QH which was not a bad play but one made with little foresight as the contract looked too easy to handle.