The South player in the deal below was not only a known joker but he was also known as a very fine player. The same can be said for both East and West.

W/All		♠	A J 10
		♥	9 8 3
		♦	J 9 4
		♣	10 7 6 2
♠	5 4 2			♠	K
♥	A 10 7 5			♥	Q J 4 2
♦	5 3			♦	8 7 6 2
♣	K Q J 3			♣	A 9 8 5
		♠	Q 9 8 7 6 3
		♥	K 6
		♦	A K Q 10
		♣	4

¹ Five or more spades

The play took about 23 seconds. West led the ♣K and continued with the ♣J. South ruffed and played a small spade to the ♠A (!). Nobody moved a muscle when East's ♠K came tumbling down. After two more rounds of trumps declarer played a heart to his ♥K, losing to West's ♥A. Next South claimed for the loss of one more heart.
'Next time you'd better keep your cards closer to your chest', South told East - to the astonishment of a young kibitzer sitting behind South. However, the kibitzer missed South's winking at East.
'Sorry, partner', East grinned, 'I will get myself reading glasses as soon as possible, so I can keep the cards closer to my chest.'
'So you should', West agreed but his wink went unnoticed by the kibitzer as well.
Later at the bar the kibitzer reported the deal to the bystanders. 'Can you believe it, this guy South peaking in East's cards, admitting it and EW not bothering!'

The bystanders knew better and quickly opened his eyes: 'South went up with the ♠A for a purely technical reason and EW knew. Their popular theatre was meant for the gallery, meaning you.'
Which technical reason, you ask? South could only be defeated if he lost both the ♠K and two hearts. If the ♥A was favourably placed, with East, the contract was unbeatable. South therefore reasoned as follows: 'Suppose the ♥A is unfavourably placed, with West. He is known to have the ♣KQJ and the ♥A then. He has not opened, so - still assuming he has the ♥A - he cannot have the ♠K as well. If so, my only chance is for East to have the bare ♠K.'
But what if the ♠K had been in West? Well, he would have had the ♣KQJ and the ♠K then, meaning he could not have had the ♥A and South would always make his contract. By refusing to finesse the ♠K he would then have sacrificed the overtrick, that is all.

This kind of strictly logical reasoning often is an eye-opener for beginners at bridge. Yet this kind of deals, in which the correct line of play is based on a 'necessary assumption' (as Terence Reese called it in The Expert Game), is quite common.

W/All		♠	K J 5
		♥	7 4 3
		♦	A 10 4 2
		♣	K J 6
♠	8 4 3			♠	7
♥	K Q J 5			♥	A 10 9 2
♦	K 8 6			♦	7 5 3
♣	Q 9 5			♣	A 10 8 7 3
		♠	A Q 10 9 6 2
		♥	8 6
		♦	Q J 9
		♣	4 2

West led the ♥K, thereby denying possession of the ♥A and requesting East to either play the ♥J (if he had it) or show his distribution (if he did not have the ♥J). So East played the ♥10 (high-low showing an even number). West continued with the ♥J, East played the ♥2. West switched to the ♣5 and South faced an all too common dilemma: the king or the jack?
Again he wasn't bothered at all. Unhesitatingly he inserted the ♣J, East winning with the ♣A. Shortly afterwards the finesse of the ♦K succeeded and South duly made his contract.
South turned to East. 'Not having reading glasses has cost you a huge amount of points by now', he started.
This time the kibitzer did not fall for it: 'I get it, by playing the ♥2 in the second trick East asked for a club switch. So he was sure to have the ♣A, maybe the ♣Q as well but not the ♣Q only.'
East shook his head. 'No, having the ♣Q10 I would have asked for clubs as well, my partner would smoothly have underled the ♣A then.'
'After all, we need to cash two quick tricks in clubs', West joined in. Then, winking, he added: 'It really is those spectacles, you know.'
The kibitzer felt he was taken for a ride but didn't know how.
Later at the bar his eyes were opened once again: 'South had lost two heart tricks already. Suppose the ♦K was wrong, in East. Since South still had the ♣A to lose, he would not have stood a chance then. So he had to assume the ♦K to be with West. West was already known to have the ♥KQJ. Add the hoped for ♦K and West has nine points. Since he has not opened, he cannot have the ♣A as well. ♣Q on the other hand was possible - just. So South could only hope for the ♦K and the ♣Q with West and the ♣A with East. And he was rewarded. Nothing to do with reading glasses but a necessary assumption: the ♦K in West.'

To be continued