user25701: I have been studying the King's Indian Attack a bit recently, and have started reading through Neil McDonald's Move by Move book on it.
Earlier today I played a game against a 2100 on Lichess (I am around 1700 rapid) and attempted to play the KIA against my opponent's e3 Sicilian. After the first few moves I pushed my e4 pawn to e5 like the McDonald book talks about and then my opponent played 10..f6, leaving no way for me to keep my pawn. I thought that if this were viable I must have messed up the move order and quickly resigned after losing my only central pawn. Checking it with the engine, it looks like a slight inaccuracy from my opponent, going from about a -0.5 evaluation to 0.5 in my favour. But why is this? How am I supposed to "punish" this decision?
[Event "Rated Rapid game"]
[FEN ""]
[Date "2021.04.13"]
[Result "0-1"]
[UTCDate "2021.04.13"]
[UTCTime "04:29:14"]
[WhiteRatingDiff "-2"]
[BlackRatingDiff "+1"]
[Variant "Standard"]
[TimeControl "300+8"]
[ECO "B40"]
[Opening "Sicilian Defense: French Variation"]
[Termination "Normal"]

1. e4 c5 2. Nf3 e6 3. d3 d5 4. Nbd2 Nc6 5. g3 Nf6 6. Bg2 Be7 7. O-O O-O 8. e5 Nd7 9. Re1 Qc7 10. Qe2 f6 11. exf6 Nxf6 0-1

I looked in the database for similar games but at least in the masters' database I'm having difficulty finding the common theme in white's winning plan. From what I have seen, I'm thinking black's e6 pawn becomes a target now that it's sad and alone, and maybe if a c4 pawn break was built up, the c4-f7 diagonal to the king is dangerous? Would anyone with a better understanding of chess be able to tell me if this is correct or if there might be anything else wrong with ..f6?

user15049: You are right that e6 is your target and also that a winning plan is not trivial to find, that is because there is no clear win. The weak square e5 and the weak pawn e6 often do not guarantee a win, but usually white has a long-lasting slight advantage.
f7-f6 attacks a pawn chain (ok, this is not really a pawn chain, but it would be, if your pawns were on c3 and d4) from the front (the e5 pawn). c7-c5 (or b7-b5-b4) attacks it at the base (the d4 pawn, which is not on d4 in this example). c7-c5 is less weakening than f7-f6, because d4xc5 does not weaken the d5 pawn, but e5xf6 weakens the e6 pawn. Still, f7-f6 is often ok (this view has changed during chess history), when black gets dynamic counterplay. We see these ideas often in the French defense. Sometimes black manages to play e6-e5, completely freeing his game, though the then slightly weak d5 pawn is something black has to take care of.
So in this game you should have played calmly for control of the e5 stop square (see Kmoch:"Pawn Power in Chess", diagram 75), bring your bishop to h3, your knights to f3 and e5, and triple your heavy pieces on the e-file.
Once all your pieces are placed well, and his are bound to the e6 pawn, open a second front, for example with a2-a3 and b2-b4 or with c3-c4, or by pushing your pawns on the king side. This is according to Dworetzkys "Theory of the two weaknesses", which says that one weakness (e6 in this case) can be defended, but two or more weaknesses often can not.
Edit: And what you obviously should not do is resigning just because you have no idea what to do. In such a case, check out which of your pieces are not well-placed, and improve their position (Rowson: "Talk with your pieces"). For example, I would have played 12.Ng5! and on 12... e5 13.c4!, and if he plays 13...d4 then I have a beautiful square e4 for the knights. Looks won for white, at least in a human vs. human game. For example, the bishop c1 (and therefore Ra1) are bad pieces here, so play (the slightly unusual) 12.b3! in order to control d4 and e5 with the bishop b2.

user12873: The ...f6 move is definitely a playable idea in many KIA positions, and it decreases your chances for building up a steady kingside attack. It also opens the f-file for Black's rook, and if you're not careful you could find yourself being attacked on the kingside. However, the drawbacks of ...f6 are that it weakens the e6-pawn, as well as the e5-square. So your plan would be to clamp down on e5, ensuring that the e6-pawn remains a weakness. If Black can get away with pushing ...e5, things won't be good for you.
On that note, I like the c4 idea you suggested. This puts pressure on the d5-pawn, discouraging the e6-pawn from moving (as it would weaken the d5-pawn). Although after playing c4, I wouldn't advise immediately playing cxd5, as this will just relieve Black of his backwards pawn after ...exd5. Instead, it's better to just leave the pawn on c4, where it will continue to pressure the pawn chain. If Black slips up at some point, such that he is unable to recapture on d5 with ...exd5 (maybe some pin on the e-file), then you can go ahead with cxd5.
If possible, develop your c1-bishop to f4, helping to watch the e5-square. Alternatively, the bishop could develop to b2 with the same purpose. Black could block the bishop with ...d4, but then this will give your d2-knight access to the c4-square, allowing it to control e5. So if you play Bb2, it's better not to play it in conjunction with pushing your pawn to c4. Note that ...d4 would also open up your g2-bishop on the h1-a8 diagonal.
As mentioned earlier, Black might try attacking on the f-file. So h3 is a move you could consider, controlling g4 and stopping any ...Ng4 ideas. Although at the same time, h3 could be used by your light-squared bishop in order to attack the e6-pawn. The bishop would be a bit vulnerable here, and it being off g2 weakens the f3-knight, so maybe only play this move when you think it's definitely worth it to attack the e6-pawn further. Another option for attacking the e6-pawn is Ng5, although like Bh3 this isn't really a move that puts your piece in a long-term stable position. And if you play Ng5 prematurely, you weaken your control over the e5-square, potentially allowing Black to push ...e5. However, one idea to consider is moving the f3-knight, pushing your f-pawn to f4, and then retreating the knight to f3. This will leave you with additional control over the e5-square.

25701: <p>I have been studying the King's Indian Attack a bit recently, and have started reading through Neil McDonald's Move by Move book on it.</p>
<p>Earlier today I played a game against a 2100 on Lichess (I am around 1700 rapid) and attempted to play the KIA against my opponent's e3 Sicilian. After the first few moves I pushed my e4 pawn to e5 like the McDonald book talks about and then my opponent played 10..f6, leaving no way for me to keep my pawn. I thought that if this were viable I must have messed up the move order and quickly resigned after losing my only central pawn. Checking it with the engine, it looks like a slight inaccuracy from my opponent, going from about a -0.5 evaluation to 0.5 in my favour. But why is this? How am I supposed to &quot;punish&quot; this decision?</p>
<pre><code>[Event &quot;Rated Rapid game&quot;]
[FEN &quot;&quot;]
[Date &quot;2021.04.13&quot;]
[Result &quot;0-1&quot;]
[UTCDate &quot;2021.04.13&quot;]
[UTCTime &quot;04:29:14&quot;]
[WhiteRatingDiff &quot;-2&quot;]
[BlackRatingDiff &quot;+1&quot;]
[Variant &quot;Standard&quot;]
[TimeControl &quot;300+8&quot;]
[ECO &quot;B40&quot;]
[Opening &quot;Sicilian Defense: French Variation&quot;]
[Termination &quot;Normal&quot;]

1. e4 c5 2. Nf3 e6 3. d3 d5 4. Nbd2 Nc6 5. g3 Nf6 6. Bg2 Be7 7. O-O O-O 8. e5 Nd7 9. Re1 Qc7 10. Qe2 f6 11. exf6 Nxf6 0-1
</code></pre>
<p>I looked in the database for similar games but at least in the masters' database I'm having difficulty finding the common theme in white's winning plan. From what I have seen, I'm thinking black's e6 pawn becomes a target now that it's sad and alone, and maybe if a c4 pawn break was built up, the c4-f7 diagonal to the king is dangerous? Would anyone with a better understanding of chess be able to tell me if this is correct or if there might be anything else wrong with ..f6?</p>
 15049: <p>You are right that e6 is your target and also that a winning plan is not trivial to find, that is because there is no clear win. The weak square e5 and the weak pawn e6 often do not guarantee a win, but usually white has a long-lasting slight advantage.</p>
<p><strong>f7-f6</strong> attacks a pawn chain (ok, this is not really a pawn chain, but it would be, if your pawns were on c3 and d4) from the front (the e5 pawn). <strong>c7-c5</strong> (or <strong>b7-b5-b4</strong>) attacks it at the base (the d4 pawn, which is not on d4 in this example). <strong>c7-c5</strong> is less weakening than <strong>f7-f6</strong>, because <strong>d4xc5</strong> does not weaken the d5 pawn, but <strong>e5xf6</strong> weakens the e6 pawn. Still, <strong>f7-f6</strong> is often ok (this view has changed during chess history), when black gets dynamic counterplay. We see these ideas often in the French defense. Sometimes black manages to play <strong>e6-e5</strong>, completely freeing his game, though the then slightly weak d5 pawn is something black has to take care of.</p>
<p>So in this game you should have played calmly for control of the e5 stop square (see Kmoch:&quot;Pawn Power in Chess&quot;, diagram 75), bring your bishop to h3, your knights to f3 and e5, and triple your heavy pieces on the e-file.</p>
<p>Once all your pieces are placed well, and his are bound to the e6 pawn, open a second front, for example with <strong>a2-a3</strong> and <strong>b2-b4</strong> or with <strong>c3-c4</strong>, or by pushing your pawns on the king side. This is according to Dworetzkys &quot;Theory of the two weaknesses&quot;, which says that one weakness (e6 in this case) can be defended, but two or more weaknesses often can not.</p>
<p>Edit: And what you obviously should not do is resigning just because you have no idea what to do. In such a case, check out which of your pieces are not well-placed, and improve their position (Rowson: &quot;Talk with your pieces&quot;). <del>For example, I would have played <strong>12.Ng5!</strong> and on <strong>12... e5 13.c4!</strong>, and if he plays <strong>13...d4</strong> then I have a beautiful square e4 for the knights. Looks won for white, at least in a human vs. human game.</del> For example, the bishop c1 (and therefore Ra1) are bad pieces here, so play (the slightly unusual) <strong>12.b3!</strong> in order to control d4 and e5 with the bishop b2.</p>
 12873: <p>The ...f6 move is definitely a playable idea in many KIA positions, and it decreases your chances for building up a steady kingside attack. It also opens the f-file for Black's rook, and if you're not careful you could find yourself being attacked on the kingside. However, the drawbacks of ...f6 are that it weakens the e6-pawn, as well as the e5-square. So your plan would be to clamp down on e5, ensuring that the e6-pawn remains a weakness. If Black can get away with pushing ...e5, things won't be good for you.</p>
<p>On that note, I like the c4 idea you suggested. This puts pressure on the d5-pawn, discouraging the e6-pawn from moving (as it would weaken the d5-pawn). Although after playing c4, I wouldn't advise immediately playing cxd5, as this will just relieve Black of his backwards pawn after ...exd5. Instead, it's better to just leave the pawn on c4, where it will continue to pressure the pawn chain. If Black slips up at some point, such that he is unable to recapture on d5 with ...exd5 (maybe some pin on the e-file), then you can go ahead with cxd5.</p>
<p>If possible, develop your c1-bishop to f4, helping to watch the e5-square. Alternatively, the bishop could develop to b2 with the same purpose. Black could block the bishop with ...d4, but then this will give your d2-knight access to the c4-square, allowing it to control e5. So if you play Bb2, it's better not to play it in conjunction with pushing your pawn to c4. Note that ...d4 would also open up your g2-bishop on the h1-a8 diagonal.</p>
<p>As mentioned earlier, Black might try attacking on the f-file. So h3 is a move you could consider, controlling g4 and stopping any ...Ng4 ideas. Although at the same time, h3 could be used by your light-squared bishop in order to attack the e6-pawn. The bishop would be a bit vulnerable here, and it being off g2 weakens the f3-knight, so maybe only play this move when you think it's definitely worth it to attack the e6-pawn further. Another option for attacking the e6-pawn is Ng5, although like Bh3 this isn't really a move that puts your piece in a long-term stable position. And if you play Ng5 prematurely, you weaken your control over the e5-square, potentially allowing Black to push ...e5. However, one idea to consider is moving the f3-knight, pushing your f-pawn to f4, and then retreating the knight to f3. This will leave you with additional control over the e5-square.</p>
