visayanbraindoctor: <chancho: What would capa think of this game if he were alive...>
'We regret Giris's blunder; but due to the tricky nature of the position and his desire to secure the draw by perpetual, we understand how he could have fallen for the illusion of a mistaken combination.'
This is a typical example of a missed tactic (also called an oversight). It's a mistaken combination wherein Giri misses a zwichenzug tactic Qh2, without which the game immediately ends in a perpetual. The human mind seems programmed to tend to miss these little tricks. Giri expected that Yu would have to capture the bishop and considered no other option.
AFAIK in Kotov's book, he discusses analysis trees and their nature. Some look like pretty little trees with well demarcated straight branches; others look like thick bushes. I think these missed tactics occur because the human brain does tends to automatically exclude certain moves from its list of potential candidates.
Every one can fall prey to this phenomenon, sometimes spectacularly. Recent spectacular ones are Morozevich vs E Inarkiev, 2014 41.. Rc1, and the double blunder in the Carlsen vs Anand WC match which every one must have already seen.
As a chess player loses focus (tiredness, excitement, impatience, lack of or too much confidence, distractions, and so on), I believe the chances for this missed tactic phenomenon increases. Giri must have felt tired or got too excited over what he saw as a potential draw in the bag; and so failed to examine other options or branches in the analysis tree.
I recently made a comment in O Bernstein vs Capablanca, 1914 about this. From several moves at the origin of a series of tactical captures and because we are programmed to consider back rank checks as all important, the human brain tends not to even consider 29... Qb2, the equivalent of a mental mouse slip.
Regarding Capablanca, at his prime he seems to have been the only player in history who never fell to this phenomenon resulting in a lost position. But even he finally did against Reti in 1924. Even then he rarely would do so for the rest of his career except in AVRO 1938.