First of all I think the example given by Purdy is too open ended.
(look at the debate above.)
There are 100's of other more drastic and instructive examples he could have used.
So why did Capa play 9.Nc3 instead of 9.b4?
According to Nimzovitch in the Tournament book Capa was depressed
over the World Title squabble and the fact it was Bogoljubov who was
to play Alekhine. This explains his up and down results in this tournament.
(He lost a piece in 10 moves v Samisch then dug in forcing Samisch to play 60+ moves.)
At the time this game was played Capa had a a nice P.5 W.5 plus v
Bogoljubov so he slipped into I'm going to win anyway mode.
Did He moved too quick or paid little attention to the opening?
In the Samisch game he arrived 55 minutes late and according to Samisch
was playing the opening whilst reading a letter!.
If this is the sort of disrespect he showed towards Samisch what was he
like v Bogoljubov a player who Nimzovitch says in the tournament Book
Capablanca regarded none too highly.
But let us suppose Capa saw 9.b4 Ncxe4.
10.Qc2 (wake up Datafly) does not win the piece. (10.....Bf5)
It's the ugly move 10.f3...
....and if we do not stop at the piece being lost (sacced?) )we can go on.
10. f3 Nxg3 11. hxg3 a5 12. b5 Nd7 13. Bb2 f5
There is work there to be done as White.
Still winning but Black is solid - 2 pawns up and White will need to break in.
So we have Capa sitting there facing an opponent he does rate who may be
willing to sac a Knight for two pawns.
"This is possibly a positional trap. Typical Bogoljubov trickery - playing for
opening traps - Alekhine will murder him. I'll ignore it I am going to win anyway."
What if the Knight does not take on e4, The a1 Rook is look non-too happy,
The Knight drops back...have I loosened my Queenside leaving myself open to a5?"
and so Capa plays 9.Nc3. There is nothing wrong with a developing move.
All good players out there have felt the same (don't get involved
in a stramash - there is no need) when playing a so called weaker player.
Play it safe and wait for the blunder is the way to go.
As the game pans out we see the blunder never came and we witness Capa
resorting to risky middle game complications ( a rarity for him) in an effort to
try and win and this nearly blows up his face.
Capablanca - Bogoljubov, Carlsbad 1929.
1. d4 Nf6 2. c4 g6 3. g3 Bg7 4. Bg2 O-O 5. e4 d6 6. Ne2 Nbd7 7. O-O e5 8. d5 Nc5 9. Nbc3 a5 10. h3 b6 11. Be3 Qe7 12. a3 Nh5 13. b4 axb4 14. axb4 Rxa1 15. Qxa1 Na6 16. b5 Nc5 17. Qa7 f5 18. Bxc5 dxc5 19. d6 Qxd6 20. Rd1 Qe6 21. exf5 Qxf5 22. Ne4 Nf6 23. g4 Qe6 24. Qxc7 Nxe4 25. Bxe4 Qf6 26. f3 h5 27. Rd6 Qh4 28. Kg2 hxg4 29. hxg4 Bxg4 30. Rxg6 Bh3+ 31. Kg1 Qe1+ 32. Kh2 Qxe2+ 33. Kxh3 Rxf3+ 34. Bxf3 Qxf3+ 35. Rg3 Qh1+ 36. Kg4 Qe4+ 37. Kh3 Qh1+