In Elements of Positional Evaluation: How the Pieces Get Their Power (2010), Dan Heisman defines flexibility as one of seven positional concepts. Zwischenzug (an in-between move) often reveals flexibility in action. I failed a tactics problem by overlooking a zwischenzug. First, examining one plan that failed, I rejected it and found another plan. The second plan was correct, but a part of the first plan remained valuable. My wholesale rejection of the failed plan led to inflexibility in my thought process. This inflexibilty, when faced with an unexpected response, was the source of a blunder.
Black to move
Problem 77164 on Chess Tempo
Instantly, the check 1...Rc1+ bears examination. This move leads nowhere and must be rejected. Chasing pawns seems futile as well, but the knight is trapped.
I found the line 1...Re8 2.Nxd4 Rd8 when White wins a piece.
Playing 1...Re8, CT then confronted me with the unexpected 2.Rxd4. I proceeded with the original plan to win the knight and blundered. This game losing blunder (and tactics training failure) took me five seconds. Even 2...Rxd4 3.Nxd4 Rxe5 was superior too my horrid 2...Re6??
The correct move was 2...Rc1+, the first move that I examined, but played one move later. Such bull-headed pursuit of one idea when new unexamined circumstances appear on the board have been the cause of more than one failure in tournament play. The antidote to this failure is to create a problem set of zwischenzug problems on CT and spend several hours of deliberate practice solving them.