Why is black playing ...f6 to attack the e5 pawn a bad move in the King's Indian Attack? 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 &quot;punish&quot; this decision?
[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

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?
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:&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.
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 &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.
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;). 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.