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I just failed a puzzle at chess.com, despite being 2 moves away from check mate. I am quite sure that there is no move I could have made to get check mate in 1 move, so I am wondering how I failed.

I just looked at the suggested solution, which would be moving to g3 instead, why is that better than my move?

Move classified as incorrect

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  • why don't you just check on lichess? you can even use chessvision to get the FEN
    – BCLC
    Dec 5 '21 at 20:08
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g3 is a better square for the Knight because it blocks White's g-pawn and so prevents White playing g3 or g4.

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  • The knight additionally has protection at g3 from the h4 pawn but is undefended at f2. That's not a reason to make the move alone, but it does make it a generally stronger position.
    – J...
    Dec 3 '21 at 14:02
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As pointed out by Michael West, 1...Nf2 provides White the opportunity to exploit White's overwhelming advantage whereas 1...Ng3 is a forced checkmate in three (i.e., Black has a guaranteed win).

Black is down too much material and has no compensation if they cannot force mate. After 1...Nf2??, Black is utterly lost.

Stockfish 14+ NNUE confirms this (+9.8, depth = 27, 8115k nodes/s). Despite the low depth, the example lines provided illustrate the point.

[FEN "8/2Q2pk1/3p2p1/NP1Np3/4n2p/7P/6PK/r7 b - - 0 1"]

1...Ng3! 2. Qxf7+ Kxf7 3. b6 Rh1# {Black wins} (1...Nf2?? 2. g4 hxg3+ 3. Kxg3 Ne4+ 4. Kf3 Ng5+ 5. Ke2 Ne6 6. Qxd6 Kh7 7. Nc4 e4 8. Qe5 Ra4 9. Nf6+ Kh6(2. g3 Ne4 3. gxh4 Ra2+ 4. Kg1 Ra1+ 5. Kg2 Ra2+ 6. Kf3 Nd2+ 7. Ke3 Nf1+ 8. Ke4 Ng3+ 9. Kd3 e4+)) 

Note: Diagram from Black's point of view to match OP's diagram.

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  • 6
    It's not about White having "counterplay". Black is completely lost in terms of everything other than the forced mate: white is up a huge amount of material. If black fails to deliver forced mate, allowing white to save the king via g3 or g4, black has no mate and will lose promptly. You don't need an engine to see that at all.
    – YiFan
    Dec 3 '21 at 13:39
  • @YiFan Agreed. I wrote the answer quickly. I've updated the answer to reflect your comment. Do you agree with my language now? Dec 3 '21 at 15:03
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    Sure, it's better now I guess. I'm not belittling people who use engine analysis, and there are many positions where it is helpful, especially if it is a very tactically complicated position. On the other hand, to improve one's chess ability it is necessary to learn how to evaluate positions without an engine. This position (after ...Nf2??) is extremely easy to evaluate once you see there's no forced mate, and one's first thought should never be to look to an engine especially in such positions when the correct evaluation is not difficult to see.
    – YiFan
    Dec 3 '21 at 15:17
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    In terms of explaining why the position is winning for white, I find "black is down too much material and has no compensation if they cannot force mate" to be much more convincing than "Stockfish 14 NNUE evaluates it as +9.8 at depth 27 and 8115k nodes/s", don't you? The former allows for real understanding, the latter doesn't.
    – YiFan
    Dec 3 '21 at 15:21
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    "(e.g., Black has a guaranteed win" *i.e. Dec 3 '21 at 23:08
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For future puzzles provided by chess.com specifically, the puzzle controls also offer engine analysis, which can be very helpful for figuring out why you move is incorrect. You can see the computer refute your move by trying it out in the analysis. I've highlighted the button in a yellow box:

Engine analysis tool

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