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Wikipedia defines a blunder as follows:

In chess, a blunder is a very bad move. It is usually caused by some tactical oversight, whether from time trouble, overconfidence or carelessness.

Here when I use the engine from chess.com to analyse a game, the engine considers black's move Qf5-c2+ as a blunder and Qf5-h3 is considered as the best move. I failed to see why Qc2+ is a blunder; can anyone help me to explain?

By the way, is this game a draw before Qf5-c2+ (assuming both sides make best moves)?

enter image description here

Edit: I am still curious about this position; anyone can help me with a deep engine analysis and see if it is a draw?

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I agree with Stephen's points however...

... in normal times, with no previous repetition, Qç2 is actually a good try to win the game!

The plan to win this game is to bring the Black King to g3 in order to mate the White King. Meanwhile Black should protect the b7-pawn, which will be attacked by the Bg4-c8 maneuver.

First, I didn't see how White defends against Black's plan because in practice it is very hard to defend this position. Here is an illustration:

[fen "8/1p2k2p/1Pp5/2PpNq1P/3P4/4PB2/4K3/8 b - - 0 1"]

1... Qc2! 2.Ke1 Kf6! 3.Bg4! {the best idea to draw the game} Qg2! (3...Kg5 4.Bc8 Kxh5 5.Bxb7=) 4.Bc8 Qg7 5.Bg4? (5.Kd2 Kg5 6.Nd3!! {see the following diagram}) Kg5 6.Ke2 Kh4 7.Kf2 Qf8 8.Kg2 Qf6 9.Bf3 (9.Bc8 Kxh5 10.Bxb7 Qg7-+) Qg5 10.Kf2 Qg3 11.Ke2 Qh2 12.Kd3 Qb2 13.Bg4 (13.e4 {is not so effective} Qb3 14.Ke2 Qc3! 15.exd5 Qxd4 16.Nxc6 {sets a nice trap} bxc6 17.dxc6 Kg3! (17...Qxc5 18.c7=)18.c7 Qf2-+) Kg3! 14.Bc8 Kf2 15.Bxb7 Ke1-+ {and the mate follows soon} 16.Nf3 Kd1 17.Bxc6 Qb3#

Now, I am not so sure it's winning because White has a fantastic fortress, which consists of transferring the Knight to f4, via d3, to prevent the Black King to enter.

[fen "2B5/1p4qp/1Pp2k2/2PpN2P/3P4/4P3/8/4K3 w - - 7 5"]

1.Kd2 Kg5 2.Nd3!! Kxh5 3.Nf4 Kh4 4.Ke2 Qe7 (4...Kg3?? 5.Nh5) 5.Kf3 {and the Black king cannot enter into g3!}

Black can improve its position by pushing the pawn to h4, bringing the King back to d8 to chase the Bishop and centralizing the Queen. It can also set some traps. It's horrible to defend for White, but I am not sure this is a forced win.

[fen "3k4/1p6/1Pp5/2Pp4/3PqN1p/4P2B/5K2/8 b - - 75 49"]

1... Qc2 2.Kf3 Qh2 3.Bg2?? (3.Bf5 {and I don't see a clear win}) Qg3 4.Ke2 Qxg2!! 5.Nxg2 h3-+

To capture the h5-pawn is probably not useful because the h7-pawn can go until h4 and then it is stopped. Moreover, the h4-pawn prevents the Black King from entering. However, so far I have not been able to find another winning plan for Black! But, I'm trying...

[fen "2B5/1p4qp/1Pp5/2Pp2kP/3P4/3NP3/4K3/8 b - - 10 6"]

1... Kh4!? 2. Nf4 Kg3 3.Nd3! {the Knight is a super defender} Qf7 4.Kd2! Qe7 5.Ke2! {to close the door for the King}
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  • Many thanks for your effort analysing the game! I think whether this game is winning for black or a draw determines whether Qc2+ is a blunder or not. If white is winning, then Qc2+ which results in an immediate draw is a blunder; if the game is a draw anyway, I would not call Qc2+ a blunder: what differnece does it make?
    – Zuriel
    May 26, 2020 at 21:54
  • So far I was not able to find a clear win...
    – Kortchnoi
    May 26, 2020 at 22:51
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The engine considers Qc2+ a blunder because it's a draw by repetition. (I think the position is probably a draw anyway, but Black could at least try for a win.) The problem is that you have already reached this position twice before. If this was the first time you had reached this position, there would be no problem: Qc2+ is actually a good move in itself. But since you have kept repeating the position instead of making progress, you now need to play something different, such as Qh3.

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  • Thank you! Your answer is very clear. A related question: if the position is a draw anyway, should a move causing three fold repition be considered a blunder?
    – Zuriel
    May 26, 2020 at 13:23
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    @Zuriel The engine isn't smart enough to see it's a draw (it gives -2.91 as evaluation, which is correct if you count points). For a computer, it's hard to see Black can't make progress because White has no weaknesses.
    – Glorfindel ♦
    May 26, 2020 at 14:07
  • Thank you @Glorfindel for the clarification! I used to think the engines are much smarter than most human players and now I change my mind. I guess no human coach should call Qc2+ a blunder.
    – Zuriel
    May 26, 2020 at 15:37
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    @Zuriel: Well, it's a higher-level blunder if you made it without realising it would end the game!
    – TonyK
    May 26, 2020 at 16:34
  • I guess if you've offered White the draw and they turned it down, then completing the repetition is no more of a blunder than offering the draw was. Since you're not at a disadvantage, the computer's telling you not to deliberately play for a draw, instead it thinks you should at least explore h3. Seems legit advice (or at least not especially bad advice). Unless you have a bus to catch or something.
    – Steve Jessop
    May 26, 2020 at 17:56

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