In this game, Ryu Shikun White was fighting a one-sided ko in the top left over the life of a black group. Black, Oya Koichi, played 291 as a ko threat. Obviously White has to connect at A. Ryu carelessly played at B, and Oya promptly cut at A, killing a spectacularly large group.
We've all been there. But then so has Ryu. This negligence sheds new light on his famous dispute in the 26th Kisei Final. There, during the dame filling at the end of the game he carelessly overlooked an atari by O Rissei and so lost a game he should have won by 3.5 points. Ryu claimed initially he thought they had agreed the game was over and so the order of moves didn't matter. But O said he hadn't agreed it was over, and he hinted strongly that it was not the first case of carelessness by Ryu. Now we know he was right.