Greed. What a horrible, horrible thing when you play a chess game. When we learn the game, we are taught that gaining material is good because this is often how one beginner overplays another. Yet, it comes the time that one has to look at the position for what it is: material, certainly, but also piece position, pawn structure, and dynamic opportunities.
Things go wrong when you favour one of them without making an objective assessment of the position. Here, I will give you an example!
mw1983 - Me! chess.com, Jan 2022
1.d4 Nc6!?
I must tell you that when I play online chess, I purposely play bad (but creative!) openings to test the understanding of my opponent rather than his knowledge of opening theory. And to have some fun :)
2.d5 Ne5 3.f4 Ng4 4.e4 d6 5.h3 Ng4-f6
White played the opening energetically and has already a positional advantage. Surely, by moving many pawns he has created some potential weaknesses, but how am I going to exploit them after having neglected the development of my pieces? Basically, Black has no activity.
6.Nc3 e5
Black needs a bit of the centre as well!
7.dxe6 Bxe6 8.Nf3 d5!?
Probably, 8.Be3 would have been better because now 8...d5 is not so good (there is no knight on f3 to be captured - see text). Josif Dorfman, a strong grandmaster and a trainer, likes to point out that whenever one player has some positional advantage, he must switch to prophylactic thinking to maintain his advantage. Instead, the player who has the inferior position should look for dynamic opportunities (because strategically he has fewer chances against correct play).
9.f5 dxe4 10.Qxd8+ Kxd8 11.fxe6 exf3 12.exf7+ Kxf7 13.gxf3 Bc5
A fairly concrete line that required only a bit of calculation.
14.Bc4+ Kg6 15.Bf4 Nh6
White advantage his clear, but he also some problems. For instance, the unsafe position of his king, that cannot castle either ways. To solve this problem, logical would have been 16.Bd3+ to play 17.0-0-0 next.
16.Bxc7? Rhe8+ 17.Kf1 Rd2?!
Greed! White accepts to stay with his king in the center in exchange of the mere c7 pawn. Giving Black so much counterplay is just nonsense. And I have also missed the opportunity to play the strong 17...Nf5 threatening checkmate.
18.Bd3+ Kh5?
I thought it was fine, but 18...Nf5 was even stronger for tactical reasons.
19.Bg3? Re3
The right way to defend was 19.Rh2. Now, I can play 19...Re3 before allowing White to defend the position with Ne4.
20.Ne4? Rxf3+ 21.Ke1Rdg2?
It was too late to block the e-column, my rook had already invaded it. I also must say that Black's last move is not accurate. The concrete 21...Rd2xd3 22.cxd3 Nxe4 23.fxe4 Rxg3 was even more convincing according the engine.
22.Nxf6+ Rxf6 23.Bc7 Nf5
Bringing the last piece to the attack
24.Rh2 Re6+
It was too late for Rh2...Now Black is completely winning because after 25.Kf1 Rg1# game over. The alternative implies huge material loss (now it make sense to convert positional and dynamic advantage into material! But it did not at move 16).
25.Kd1 Ne3+ 26.Kc1 Rg8+ 27.Kd2 Rxa1
And Black has got a full rook. The rest was just trying to avoid being flagged by dirty play :)
Perhaps not 100% precise, but effective!
28.Be2+ Kh4 29.Kc3 Nd5+ 30.Kc4 Nxc7 31.Kxc5 Re1 32.Bd3 Rc6+ 33.Kd4 Ne6+ 34.Kd5 Nf4+ 35.Kd4 Nxd3 36.Kxd3 Rd1+ 37.Ke2 Rcd6 38.Ke3 Re1+ 39.Kf4 Rde6 40.Re2 Rf1+ 41.Rf2 Rxf2#
In include the link to the game as well.