In considering any move, whether the piece moved can be captured there is a first level disqualification. When does one move on to the next level? How do you know when to ask, "Sure, both K or P can capture him there, but then I can check with this fourth piece...(?)"

At the gate, c6 isn't covered yet by a4B, but if b5N moves anywhere, c6 becomes a "Plugged Hole" against BK's escape, guarded by a4B. Therefore, each possible move of this b5N ought to be second-level qualified...

1. N×d6! (threat = 2. Nb7+)*...c×d6 (or 1...K×d6)
2. Nd7#
If 1...K×d6, 2. Qd5#

*If 1...Qh1 (against 2. Nb7+), 2. Qa2# (guards d6N by skewer).

Every move you make should be at least second-level qualified. Once you've been acclimated to THAT, you can start to work on third-level, etc. 😳

The 67% failed here perhaps didn't consider the second level, nor had perhaps ever thought about the third level as being something even POSSIBLE to think about. 😵‍💫
Or, maybe they don't like to think that deeply, and prefer superficial thought, at most.

3 stars ⭐ ⭐ ⭐