I am not much for dogma, but here is my personal rule: any serious assessment of a chess position starts (implicitly or explicitly) with (1) the material count and then (2) the flight squares of the opposing K.

< <Manic> wrote: [snip] Quite weird that a fair number of people did not see [g8] was covered. >

I make lots of mistakes, but I rarely miss a stalemated K in an initial puzzle position.

Here's the theories I came up with...

Theory 1: we want to move the queen because she is attacked. From the starting position, white's queen is indirectly attacked by the black Bc8. When we move the Rd7 away, our queen is directly attacked. We are all conditioned to protect her majesty from attacks, so we our instinct is to move the queen away from the attack.

Theory 2: we are blinded by the strength of the b1-h7 diagonal. The winning combination strongly emphasises this diagonal, with three moves in a row onto the diagonal Rh7, Qxg6+ and Qh7#. This burns an image of the diagonal onto our brains, so that we assume that the variation after Kg8 also involves a move onto the long diagonal ... Qxg6+.

Theory 3: we are fooled into thinking that the queen is only looking to her left. The pattern of Bc8-Rd7-Qe6 leads our eyes away from the kingside, to create an optical illusion that the white queen can only move to the left.

Theory 4: 27...Kg8? 28. Qxg6# is a mating pattern imprinted on our pattern recognition memories, so we instinctively play for it. This temporarily blinds us to the fact that 27...Kg8 is illegal.

Theory 4 is the closest to my case. My thinking went as follows:

"OK, 27 Rxh7+ seems to be the move. White can't take the rook without allowing a quick checkmate via 28 Qxg6+ and 29 Qxh7#. Wait, what if black refuses the sacrifice? Nope, if 27...Kg8 then 28 Qxg6# is an even quicker mate, no need to examine that move any longer."

White to play (27.?) "Very Easy"

It took me about 10-15 seconds to see it, but it's all forced:

Once's theories are interesting.

I was first bogged down for 2-3 minutes by figuring out any potential combinations to see if there was any way to make Rxd8 work but I couldn't.

I next focused my attention of trying to find a way to get my Queen on the a2-g8 diagonal to lead to a mating combination but that turned fruitless as well.

However, it's not worth quibbling over as the material count and an objective assessment of the position give White a clear pawn plus with all the winning chances.

You are correct that White breaks the pin with 27. Rxh7+ to initiate a mating attack. However, the check comes from the decoy sham sacrifice of the Rook -- whose purpose is to force the Black King to h7 so White can complete the mate in two more moves.