user18911: In the below position, I played pawn from g7 to g5, trapping the white bishop. The computer didn't like that at all, and gives white a huge advantage. Instead, it wanted me to just simply develop my light-squared bishop.
What is wrong with my move?


user21223: In addition to the reasons why you are not doing great after g5, it seems to me that there is no urgency to trap the bishop immediately. If you start with Bg4, how can white keep their bishop safe from a future g5? There is nowhere for it to go, and if they try to create an escape route with e4 then dxe4 wins the knight instead. So g5 is still a possibility and they will now need to deal with the pinned knight somehow in order to still be able to get two pawns for a piece after it.

user17842: You get a bishop in exchange two pawns and initiative for white piece.
This is the explanation: After you go to g5, your opponent can play knight takes g5 and if you recapture the knight with your pawn, queen opponent will go to h5 and it is a check. Your pawn on g5 will be captured in the next move by your opponent queen.
Black position is vulnerable and d5 pawn is the weakness that can be exploited by white.

user19877: The problem, and it really comes down to feel and analysis, is primarily that your king position can be compromised indefinitely.
In addition, virtually all of your pieces are not "harmoniously" placed, meaning they do not help each other out at all. In every line, they just get in each other's way, and nothing defends each other. In chess, we sometimes have a piece that is not defended, but you either cannot develop, or you have multiple pieces that are not protected, or weakly defended. Combine that with a king that can be pushed around, and attacked from random squares, white is sure to win the material back via a double-attack.
Specifically, the Rh8 is hanging in some lines; the only place the Bf8 can go to is g7, where it also hangs; the Qb6 is in the way of the king running away to that square; d5 hangs allowing white to push the king to worse squares, including one that allows more tactics with e4; and even the Nc6 can be attacked strongly, and when removed, it allows tactics on that Rh8 I mentioned.
White almost has enough material just winning the two pawns, and seeing that d5 is probably a goner. Add in your king position, and loose pieces, it was an easy call to play Ng5.
Here are some sample lines:
 [FEN "r1b1kb1r/pp2p1pp/1qn2p2/3p4/3P1B2/1P2PNP1/P4PBP/R2Q1RK1 b kq - 0 1"]

 1... g5 2. Nxg5 fxg5 3. Qh5+ Kd8 4. Bxg5 Be6 (4... Bf5 5. Bh4 (5. Bxe7+ $4 Nxe7 ) 5... Bg6 6. Qxd5+ Ke8 (6... Kc8 7. Rac1 Kb8 8. Rxc6 Qxc6 9. Qe5+ Qc7 10. Qxh8 )) 5. Rac1 (5. e4 {Is also great.} Nb4 (5... Nxd4 6. Rad1) 6. a3 Nd3 7. Rad1 Nb2 8. Rd2 Qxb3 9. Rb1) 5... Bg7 6. Rc5 Qc7 7. Bxd5 Bxd5 8. Rxd5+ Kc8 9. Bf4 e5 10. dxe5 Qe7 11. Qf5+ Kc7 12. e6+


18911: <p>In the below position, I played pawn from g7 to g5, trapping the white bishop. The computer didn't like that at all, and gives white a huge advantage. Instead, it wanted me to just simply develop my light-squared bishop.</p>

<p>What is wrong with my move?</p>

<p><a href="https://i.stack.imgur.com/OdZA7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OdZA7.png" alt="enter image description here"></a></p>
 21223: <p>In addition to the reasons why you are not doing great after g5, it seems to me that there is no urgency to trap the bishop immediately. If you start with Bg4, how can white keep their bishop safe from a future g5? There is nowhere for it to go, and if they try to create an escape route with e4 then dxe4 wins the knight instead. So g5 is still a possibility and they will now need to deal with the pinned knight somehow in order to still be able to get two pawns for a piece after it.</p>
 17842: <p>You get a bishop in exchange two pawns and initiative for white piece.</p>

<p>This is the explanation: After you go to g5, your opponent can play knight takes g5 and if you recapture the knight with your pawn, queen opponent will go to h5 and it is a check. Your pawn on g5 will be captured in the next move by your opponent queen.
Black position is vulnerable and d5 pawn is the weakness that can be exploited by white.</p>
 19877: <p>The problem, and it really comes down to feel and analysis, is primarily that your king position can be compromised indefinitely.</p>

<p>In addition, virtually all of your pieces are not "harmoniously" placed, meaning they do not help each other out at all. In every line, they just get in each other's way, and nothing defends each other. In chess, we sometimes have a piece that is not defended, but you either cannot develop, or you have multiple pieces that are not protected, or weakly defended. Combine that with a king that can be pushed around, and attacked from random squares, white is sure to win the material back via a double-attack.</p>

<p>Specifically, the Rh8 is hanging in some lines; the only place the Bf8 can go to is g7, where it also hangs; the Qb6 is in the way of the king running away to that square; d5 hangs allowing white to push the king to worse squares, including one that allows more tactics with e4; and even the Nc6 can be attacked strongly, and when removed, it allows tactics on that Rh8 I mentioned.</p>

<p>White almost has enough material just winning the two pawns, and seeing that d5 is probably a goner. Add in your king position, and loose pieces, it was an easy call to play Ng5.</p>

<p>Here are some sample lines:</p>

<pre><code> [FEN "r1b1kb1r/pp2p1pp/1qn2p2/3p4/3P1B2/1P2PNP1/P4PBP/R2Q1RK1 b kq - 0 1"]

 1... g5 2. Nxg5 fxg5 3. Qh5+ Kd8 4. Bxg5 Be6 (4... Bf5 5. Bh4 (5. Bxe7+ $4 Nxe7 ) 5... Bg6 6. Qxd5+ Ke8 (6... Kc8 7. Rac1 Kb8 8. Rxc6 Qxc6 9. Qe5+ Qc7 10. Qxh8 )) 5. Rac1 (5. e4 {Is also great.} Nb4 (5... Nxd4 6. Rad1) 6. a3 Nd3 7. Rad1 Nb2 8. Rd2 Qxb3 9. Rb1) 5... Bg7 6. Rc5 Qc7 7. Bxd5 Bxd5 8. Rxd5+ Kc8 9. Bf4 e5 10. dxe5 Qe7 11. Qf5+ Kc7 12. e6+
</code></pre>
