Interesting Board #3 of final 8 teams 1st segment.

Hweinstein
1098
7
75
QJ109654
Ginossar
Q7
AQ4
AK982
K82
Wildavsky
J6
K98632
Q64
A7
Willenken
AK5432
J105
J103
3
W
N
E
S
2
P
4
P
P
P
D
3
4 South
NS: 0 EW: 0
7
A
8
5
1
1
0
Q
6
2
10
1
2
0
7
J
A
9
3
3
0
K
8
2
2
3
4
0
J
5
A
4
1
5
0
Q
K
10
Q
2
5
1
3
J
6
4
3
6
1
5
4
2
6
3
7
1
4
9
8
7
3
8
1
3
10
K
A
3
9
1
10
7
K
6
1
10
1
10 tricks claimed
N/S +420
11

This hand in USBFC played in 4 at most tables.

Surprisingly to people, a lot of declarers, most of them are known for their great card play skills, decided to take the finesse on opening lead and went down. So when I saw more than 1 great player doing this, I started to wonder why they did that and what were we missing? Isn't just winning the first and clearing trumps make the game unless split 4-1?  So I started to do some calculation but stuck at some point.

I think, 4-1 or 5-0 split is about % 32. When they take the finesse, in order this to be a danger, finesse loses (%50), hearts are 1-6 (%3.4) and RHO has the A (%50) .

In order to win the A to lose,  K will be onside (%50  but one can argue that the aspect of leading under K makes it less likely) + spades are 4-1 or 5-0 (%32)...... we may also lose a (we can not discard it on K or it does not drop or finesse does not work and I do not know how to calculate this all together)

After one can do the calculations of all of this, one has to also calculate

a-how many imps you lose by going down when other line makes (or not win when other side also goes down) when you take the finesse?

b-how many imps you gain (or not lose) by finesse when it works?

And then when you have those numbers, one needs to calculate which one is profitable in the long run. So to those who asked me about the play of these famous players in BBO, these calculations may have decided their choice of play. Perhaps someone who is good at these numbers can tell us the exact expectations of each line. I have a feeling the finesse may not be as bad as people think but I maybe wrong.

EDIT to poke Steve Weinstein:  Steve! If your table reading skills are not good enough to detect that lead was from singleton, what are they good for?  (that was a joke to Steve related to another topic, nothing mean is intended)