Master Po: When one eye is fixed on the destination, Grasshopper, you have only one eye to search for the way.
Chess Master: It only takes one lapse of concentration to snatch defeat from the jaws of victory.
In this position black was under attack but seemed to have everything covered. He is a pawn up, has the two bishops, has an open file to develop an attack on white's king when he gets out from under. Of course, white has the rooks doubled on the c-file but black's knight, rook and queen appear to be holding everything together.
Then, out of a clear, blue sky, white pounced.
Use Chess Genie to play through the attack:
1. Nc6 bxc6 [if 1. . .Nc6, 2. bc6; 1. . . Ka8 2. Nxe7]
2. bxc6 Kc7
3. Qb8! resigned [if 3. . . Kxb8, 4. c7#]