Bridge contracts are based either on bidding strength or distributional hands. But sometimes they gather their own momentum when the opponents intervene and show their strength, distribution and the probable lie of cards.
It is only at that point that the law of total tricks takes over and players tend to outbid each other so that the opponents are not allowed to play a contract at a level dictated by the law of 'Total Tricks', which says that if this combined trump combination between the two partners hands is 8, the best par contract is 8 tricks at the 2 level.
Any trump addition can subsequently raise the contract. Of course, other strength showing points and distribution patterns can raise the level much higher as in the following deal, where the bidding went as under:
One look at the dummy, and declarer can count 12 tricks if trumps break 2-2, for then he can ruff 2 diamonds after giving a diamond to the opponents, there being no losers in spades or clubs.
When declarer after playing the KC on the first trick, tried to draw trumps in two rounds, to his dismay he found west with three. Since the possibility of ruffing 2 diamond losers in the closed hand was eliminated by the adverse trump break, declarer weighed the possibility of ruffing the 3 black losers in his hand in dummy which was again quite improbable as the inference of east's 3D bid and west's failure to lead diamond marked east with 7 diamonds and therefore west with a void. If west held 3 trumps, his black suit division would be either 5-5 or 6-4. There was no way, 3 black ruffs could be achieved in dummy.
This is where the expert rises above the average player. What can be done? The expert gathers his inferential clues closely. The only lead he has at this stage is the distribution of the opponents cards in lieu of east's, 3D preventive call. Can you as south visualise any solution? With nothing else to do, the only silver lining lay in bringing about some sort of an endplay against east? East had already thrown a diamond on the second trump. Of course, first things first. The last trump had to be drawn with the jack and a diamonds led towards his hand. On JD by east forcing south to take AD, west discarded a club. The declarer played his second club honour and encashed the top spade honours of AK, noting the fall of JS from east.
At this point of time, declarer knew that in all probability, east was either exhausted of all spades, or all clubs, had no more trumps left and, from his diamond 7 carder originally dealt, was left with just a black card along with his diamonds. The vital question that still hurt the declarer was whether east held a spade or a club?
On the judgement in bridge, it is again the expert who has the potential to make a far sounder judgement than the average player. There is a reason to it. The expert works hard in his reasoning and uses all inferences available to him, which gives him the edge over others.
Looking back at the play of the AK of club and the opining lead of QC, the declarer had noted that east had started with 2C followed by 6C. Although there was no certainty that east would be showing proper count of an odd distribution to his partner by low-high, the declarer concluded that east had a club, instead of a spade, and on that basis of judgement ruffed a club in the dummy and was rewarded in his judgement when the third club followed from east.
Of course the declarer now had the defender by the scruff of the neck to endplay him in diamonds. For the last 4 cards that lay with east were all marked as KQ87 and the most vital card that made all the difference for the endplay to work was the 9D with the declarer along with his 6 of trumps and 2 spade losers of 95. Imagine the plight of east when declarer plays small diamond from the dummy. If east takes it with QD he is truly endplayed. If he tries to encash KD, it will be ruffed in hand, a spade ruffed in dummy and the 10D encashed for a spade discard. If east plays a low diamond, declarer lets it run to dummy's 10D, discarding a spade, and cross ruffs. Both ways, east is a dead duck.
My readers would still be seeking as to how south based his conclusion that east had more probability of holding a third club rather than a spade. The answer was simple on the probability number. There were 8 clubs between the opponents to the 7 spades which gave the edge of a club holding rather than a spade with east. A judgement made with open eyes than closed was better.

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North       West     East    South
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76        Q10843       J2     AK95
KQ7107      954         8     A632
10653       ---    KQJ8742      A9
AK       QJ1095        862     743
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The Bidding:

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West    North    East   South
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-         -        -      1NT
P         2D      3D       3H
P         4C       P       4D
P         4H       P       4S
P         6H     ALL
        PASS
=============================