Its not a blunder, it is an inaccuracy I believe. This means that it is a slightly worse than good (there could be better) but is not necessarily bad. Inaccuracies are easily some of the most common issues with any player and everybody makes them.
Nf6 was likely a better move which could be followed by d5.
So if this were a move being played by a master player, it wolud be considered bad? I'm trying to learn why sometimes I completely disagree with a computer analysis. You know how an analysis will assume like 5 or 6 moves into the future? Sometimes I see those as not necessairily the one a human would make. And sometimes human moves are no better or worse than computer ones ... I think... Such a hard egg to crack, this game.
Anyway, perhaps its true that although in the computer models one move at this stage may be better in the real world with human players this isn't necessairily a right or wrong move?
The computer is analyzing the move as it stands and some of the most popular working moves from thousands of past games (I think). Depending on your strategy, this may very well be a great move. But the computer doesn't know what move you'll make next.
In other words, this move just means that it was slightly worse than the best move, whatever that may be. The strongest computers in the world were once beaten by the best chess players in the world (See "Deep Blue"). This is because the creativity supplied by a human player can outstrip the logical processes of a computer. In a sense, the computer will not be able to understand the move.
2...d6 is tricky and good because it's flexible and doesn't give White any idea of how Black wants to develop. Maybe he'll play a KID or maybe he'll put his knight on e7 instead. He could play f5 or even h5 at some point.
Don't take computer analysis' "inaccuracy" comments seriously, especially in the opening.
In fact, it gives 1. e4 c5?! as inaccurate.
This d6 move is o.k, cant see anything bad about it. Black is kind of playing a closed sicilian as black. Also some computer lines are just anotated that way so that the computer engine will avoid playing moves that it does not prefer and does not mean that the move is weak as in the sense that opening books use to label blunders etcI have Hiarcs on my iPhone and quite often perfectly good moves are labeled with ?! so as not to steer the engine into positions that the author thinks are unwise.
I don't have much to add on this point except 2 moves are too early to say if it is bad... you can say a move is bad of good only after atleast 5 moves ( except in exceptional situations).
I just looked at my database and I found this position in 1437 GM level games. so it can't be bad.
I've got the same problem with computer analysis as well. Once, in response to 1.Nf3, I replied with 1...f5 as an inaccuracy(?!). Sometimes the analysis only points inaccuracies or mistakes I make, but none from my opponent when he or she clearly blundered.
1. ...f5 in response to Nf3 has been refuted by 2. d3. White obtains a large advantage by playing for a quick e4.
Go back to basic opening theory, and analyze 2. ..., d6 in terms of what it helps and what it hurts. Obviously, it shores up e5. However it blocks in the dark bishop, limiting any queenside play for that piece (perhaps it needs to be fianchettoed now). Also it makes b7 much harder to defend (think that white is putting his bishop on g3) in the long run. So you've hindered your piece development and also given yourself a long term queenside weakness. As white, I look at your play and say to myself "I'm going to pressue b7, force c6 if I can and then pressure d6"
So it's not like it's a move that immediately loses, but it's a move which hampers all kinds of normal play ideas on black's queenside. Over time, this will show up.
1. c4 e5
2. g3 d6?!
Why is d6 considered a bad move here? Its from a computer analysis of an opening. I just don't get why its ?! flagged. It doesn't seem to me like a bluder this early in the game.