Original position: After Bh5 (move I think is better because of the threat to the queen if pawn moves): After Be6 (move recommended by the engine):
2 Answers
As the engine is telling you, after
- .... Bh5
- g4 Bg6
- h4 h5 (basically forced to make space for the bishop; h6 is much worse because white will have the option to open your kingside with g5 and mate you (eventually))
- g5 Ne8 (or Nh7 which is worse)
- Qb5
is a double attack on b7 and d5, which you cannot defend both.
White will simply win a pawn which explains the ca. +1 evaluation.
With 1... Be6 you avoid this whole line.
Not only do you lose a pawn as previous answers told, but there's a strategic idea behind this too. What characterizes the position you gave is that it has opposite-side castles. On this positions, players try to pawn-storm their opponents and break their opponent's king position. With Bh5 you are giving your opponent the chance to start a pawn storm with tempo, which means you are basically allowing him to make his desired moves "for free" and succeeding easily on his plan.
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Could you please elaborate on the 'with tempo' bit? I am a beginner, I guess. Rank 1500+ on lichess with less than 100 games. Commented Apr 23, 2020 at 3:44
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6Yes, of course. We say a move "wins a tempo" when it threatens something and forces the opponent to respond. For example, if you play Bh5, then g4 wins a tempo, because you are forced to respond to the threat (you are losing your bishop!). In that sense, your opponent has made a move that improves his position (starts an attack) and forced you to "waste a tempo" at the same time (respond to a direct threat instead of playing something you willingly choose). When we say we win a tempo with a move, we say we made that move "with tempo", forcing the opponent to respond to our threat.– lafinurCommented Apr 23, 2020 at 3:57
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Extra: winning a tempo is usually a very good thing, because we are doing something we want (in the case of your game, White started an attack) and not letting the opponent respond as he likes. For example, if you had played Be6 and he played g4 then, you could have played a5 starting an attack on his king, because your bishop would not be attacked and therefore you would lose no tempo.– lafinurCommented Apr 23, 2020 at 3:59
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I am not convinced that this is really a pawn storm with an attack on the king. After h5 g5, it does not look dangerous anymore to me because the pawns are blocked. In my view, there are some intermediate moves, but the main goal is to play g5 so that the knight has to give up protection of the d5 pawn. So yes, I agree that it is with tempo that you get the pawn to g5, but I don't see an attack on the king coming, certainly not after white moves the queen to the queenside with Qb5. Commented Apr 23, 2020 at 6:26