Why does computer recommend 10. Bxf7+ and call my reasonable(?) 10. Nf3 defensive move a mistake? The computer recommends black play NxB. But why not play KxB? Does this lay black open to a multi-move combination that I just can't see? Or is it "obvious" to a GM that white simply has too much development? Or what?
Computer recommends Bf7+ sacrifice?
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You need a program you can work with to test out moves. For example, lets say you understand that after 10. bxp nxb 11. qxb white has one a clean pawn, but don't understand why 10. bxp kxb is bad. You then put that in the program, and see what the engine does. (The simple 11. pxn check wins a full piece). In other words, you need to be able to set up specific positions, not just run chess.com's analysis. I recommend smallfish or droidfish for your phone as easy ways to do this.
This is a pretty easy one for intermediate and up players, and should be doable by beginners, but eventually, no matter how good you are (unless your at least IM strength anyway), the engine will recommend a complicated tactic above your level you need some help working through. So anyone serious about understand the recommended tactics needs an engine they can work with, not just the post game evaluation run.
Mar 27, 2017
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#3
As I recommended in another thread, you need to heavily work on tactics mainly, instead of openings.
The move Bxf7+ should be quite obvious and natural for many reasons - you're winning material with a forcing sequence. If you couldn't calculate it, then it means you simply need to work on tactics a lot more.
Notice that while the biggest opening advantages the theory in the books offer you is less than a pawn's worth of evaluation, this simple tactic is the difference between a completely winning position and a highly advantageous position.
I have a cold, it's my only excuse...
Mar 27, 2017
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#5
Well I'm saying this because virtually all players at your level require heavy tactics training as the easiest (and most necessary) way to improve.
#4 "As I recommended in another thread, you need to heavily work on tactics ..."
I did both at the same time. A big theme with a white Sicilian and the move Bc4 is dropping the bishop on d5, e6 or f7 according to tactics.
So at 10. all things are in play: how well is the bishop on g4 defended; how weak is f7; what pieces are attacked; what deflections exist.
Not that is on as a move but I did even think about Bd5.
In the 10. Bxf7+ line, not sure about 12. Nd5 as I liked 12. Ne6 Qb6+ with white threatening Nxg7
11. a4 was a great move as that set in motion tactics that could not be solved.
@GodsPawn #7: Because I spend too much time studying openings, I recognised 6. .. Ng4? as definitely not standard Sicilian development for black. My response was to continue with standard Sicilian development for white, hence the castling. But I see your point, I usually chase away Ns that can only retreat with h3. I might have been in trouble if black had played e5, Qh4... certainly some tedious defensive work may have been necessary. Fortunately black played as if I had played h3 
. Also Nf3 is standard Siciklian (usually in response to .. f5) So my opening knowledge was actually blinkering me, stopping me looking for good tactics or forcing moves!
9. f4 was the first "original forcing move" I made. It seemed more forcing than 9. Bf4 as N had to move (again!) It does weaken the King's house, and Bf4 is developing a piece. So maybe Bf4 would have been better?
Mar 27, 2017
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#9
Well I recommend studying general opening principles (strategy). A player who's never seen the Sicilian theory before, but sees ...Ng4, could respond the way you did. Of course you should study general strategy.
I'm saying this because you started a thread on some 10 move deep opening in the French that I've never seen before, which had nothing to do with the game result in that thread.
Personally I'd say it's very difficult to see an attacking sacrifice combination when your most powerful piece is under threat. This is the beauty of analysing games after the event though, and discussing them with more advanced players also helps. The hope is that we can recognise these types of moves if they crop up again.
#12: Go play through the "Game of the Century"
http://www.chessgames.com/perl/chessgame?gid=1008361
that will cure you of that fear.
LuckyDan74 wrote:
Personally I'd say it's very difficult to see an attacking sacrifice combination when your most powerful piece is under threat.
Yes, that combined with the calmness produced by getting the N back on it's "natural defensive" square was too tempting, especially in a "rapid" game.
I wonder how many players of say <1400 would've seen it?
Mar 27, 2017
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#14
Understanding the reasons and ideas for why the machine says "such an such" is the bestmove is the key to realizing why. Without understand you loose regaurdless.
... the key I want to hit on is the notion that Nf3 is "reasonable". Nf3 here pins your knight and makes it purely a blocker... It is anything but reasonable.
See post #2 "The computer evaluates chess positions with help of a score. By not playing 10. Bxf7+ you went from a position worth +3.27 to +1.18 which means you're still much better after 10. Nf3 but it's a mistake because it roughly lost 2 points from what you could have."
So I think I was right in saying it was "reasonable". Obviously the bishop sacrifice is much better, but that doesn't mean my move was all bad! It's quite common for the bishop to pin the Knight, it's just here the Knight pinned itself to save the Queen... if you didn't see the bishop sacrifice, what would you do instead? Move the queen? OK - that looks more reasonable... better development... So you have a point. Where would you move the queen to? I'm tempted by Qe2, with potential to attack B and (eventually) K using the free diagonals.