Playing on BBO with a pick up partner in a team game, this interesting hand came up. I held 52 K865 AKQT8 Q7 and opened 1D in first seat. Partner bid 2C over this, and I decided not to get him too excited by bidding 2H and having him interpret this as a reverse, so contented myself with 2D to start. Partner bid 2N over this, and I bid 3N to end the auction. The opening lead was the Q of Hearts, not what I really wanted to see, and these are the 2 hands.
Not that nice spot cards in the Heart suit, but partner decided to duck the Heart lead, and the 10 appeared on his right. RHO now played a small Heart to LHO's A, and the 7 of Spades came back. And here is where partner had his blind spot.
You currently have 8 top tricks, and only have to develop 1 more to make this, at IMPS. So you need to take the safest line. Partner looked that the chance of 1 of 2 hooks working was 75%, and that gave him chances for overtricks (sigh), so put in the Q of Spades here, butchering a nice hand and play. This lost to the K, and the J of Spades came back. The hand played out for a while, and eventually partner played the Q of Clubs off board, making when the K was onside. And not even realizing the problem with the hand.
When the Spade came back, you now have a 100% line of play. Win the A of Spades, play a Diamond to board, and run the Q of Clubs. Even if it loses, they can not attack the Q of Spades, and you have an easy 9 or 10 tricks, with no down side.
It is plays like this that need to be punished with both black K's offside, to teach people about real percentages in bridge. I would rate that if played in a club game, over 90% of the people playing this hand would put in the Q of Spades, and complain about luck if both K's were offside. Then they would ask the lone +400 how they made it when everything was offside, or assume a different lead.