A good move may have an expiration date, when it is no longer good. But it may also have an optimal date, when it is best.
F. Skripchenko White
Kaputin Black
Kaluga 1960
Sicilian Defense, Najdorf Variation B94
1 e4 c5 2 ♘f3 d6 3 d4 cxd4 4 ♘xd4 ♘f6 5 ♘c3 a6 6 ♗g5 ♘bd7 7 f4 b5?!
Question 64: Is Black threatening 8...b4 9 ♘d5 ♘xe4 ?
8 ♗xf6
This sets traps. One arises after 8...♘xf6 9 e5 dxe5 10 fxe5.
Question 65: What happens after 10...♘d5 ?
8...gxf6 9 a4!
You’re right if you think ♘d5 and ♘e6 were good moves (9 ♘e6 fxe6?? 10 ♕h5 mate). But they are better if prepared by 9 a4!. For example, 9...bxa4 10 ♘e6! ♕a5 11 ♖xa4!. Or 10...♕b6 11 ♘d5! ♕a5+ 12 b4!.
9...b4
Now 10 ♘e6 ♕a5 11 ♘xf8? bxc3 is bad and 11 ♕d5 ♕xd5 12 ♘xd5 fxe6 13 ♘c7+ ♔d8 14 ♘xe6+ is only a draw (14 ♘xa8? ♗b7).
Question 66: Is 10 ♗c4 strong, in view of 10...bxc3 11 ♗xf7+! ♔xf7 12 ♕h5+ ♔g8 13 ♕d5+ ?
10 ♘d5
White’s threats include 11 ♘c6. If Black plays 10...♘c5 White is way ahead after 11 ♘c6 ♕d7 12 ♘cxb4. For instance, 12...♘xe4 13 ♕e2 f5 14 ♕c4! with the idea of ♘c7+. On 14…♕a7! White is much better after 15 ♕c6+! ♔d8 16 ♕b6+.
10...♗b7??
This stops 11 ♘c6 and renders 11 ♘xb4 relatively harmless (11...♗xe4).
11 ♘e6! resigns.
In view of 11...♕-moves 12 ♘dc7+.
Here’s a similar disaster:
Michael Redgrave White
John Steadman Black
Sydney 2007
1 e4 c5 2 ♘f3 d6 3 d4 cxd4 4 ♘xd4 ♘f6 5 ♘c3 a6 6 ♗g5 ♘bd7 7 f4 b5?! 8 ♗xf6 gxf6 9 ♘d5 ♗b7?? 10 ♘e6! ♕a5+ 11 b4! and wins (But 9...♘c5 10 c4 wouldn’t be pleasant for Black).