Two hands in Malahide last night (underdeclaring)

Hand 12 above was declared in 3N and 4NT many times . Now 12 declarers out of 30 managed less then 12 tricks. I don't get this at all as there seems to be 5 diamonds and 5 spades and 2 other tricks depending on the lead. All declarers in the room sat in West. So club or heart lead means 12 tricks.

Board 12 mainly declared in 3NT or 4N and 11 times out of 29 the declarer made 11 or less tricks.
Declarers were always West and there seems to be 12 tricks available via 5D and 5S and 2 other tricks. So I don't understand how these declarers shrank the available tricks. Clearly something is wrong. I was drawn to this hand while examining some pairs results and seeing them score badly despite their opps making sub-optimal number of tricks ..

Seems hard to make less than 12 tricks

On Hand 18 we come to a lesson I learned from Denis Dillon (RIP) one time in a Teams match.
I was declaring a 4H contract and it seemed fairly safe to make 10 tricks but I felt its a good chance
for overtricks .. So I left a spade lead run to my QUEEN ...
So Denis pipes up as he wins the King ..."Eamon I would not have done that now .. a bad thing might happen .. " ..
And two spade ruffs later and Eamon was gone down in the cold 4H ...
Now Denis was not unethical in any way .. He held singleton Heart Ace and was getting in by force
Its not like he was telling partner take your ruff and get back over to me in a side suit ..
The only problem was my greedy declarer play ..

Anyway last night I heard some mumblings around the room about some people letting a trick run to their queen and then berating themselves as they lost a ruff with a possible 12 tricks on top ..

Some were even in 6H and blew it on trick 1 ..
Others were in 4H and only missed an overtrick ..

About 12 declarers out of 29 managed to condense the tricks to 11 or less ..
..................
Meanwhile we have one of our Rivervalley Club superstars ...Shane Maxwell who to be fair has never played bridge with real cards in his hands. Shane has played various games of cards since he was about 6 years of age. However one night he had a few too many beers and challenged me about DON and Bridge in the local beer place. So I taught him DON for 10 minutes and Bridge for 15 minutes ..starting about about 1150pm ... By 1am he was at home logged on to some website and playing Bridge ..

Fast forward about 1.5 years and yesterday we found Shane with time to spare during his college course and it became clear he was having a few games of bridge  to pass the time ..

So Shane declared 3NT and managed to gather in 6 tricks .. The opposition took the first 4 heart tricks and Shane had the Heart 8 as a winner. However he somehow erred and failed to gather in the
5 diamonds 1 heart 2 spades and a club ....making 9 tricks
Shane ended up with 6 tricks

I spotted all this after playing the hand myself in 3NT and making the 9 tricks ..
So I asked Shane on social media about the hand ..
" I misrepresented my hand and I learned a lesson " ...
Now this is a poker term .. misrepresented .... but Shane failed to gather in the 9 top tricks ..
I will have to teach him a little more

However he is playing on
www.bridge-now.com

And this is a fine site to play bridge for free .. It gives you a percentage after each hand and it gives you a weekly ranking ..
Declan McKenna will be watching over his shoulder for Shanes rating this week ..

So if you want a free place to practice and compare yourself with the legendary BJ O'Brien a multiple
National champion or else with online learners Declan and Shane ...off you go and signup for free.