user19880: [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"]
[Title "Berlin Defense"]
[StartFlipped "1"]

1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. O-O Bb4?!

When White castles, Stockfish evaluates the game to be roughly equal. After Black responds with Bb4, the evaluation goes to around +1 and Stockfish labels it as an inaccuracy.
What is wrong with Black’s move? It leads to a more symmetrical position so I’m surprised that it’s considered bad.

user11144: Easy: The bishop not only shoots thin air, but also asks to be kicked around with c3, such that White wins a tempo with a move he likes to play anyway in Italian/Spanish positions to make a big center with d4. Thus, after c3 (immediately, or after Re1), White is simply a tempo up with respect to "normal" variants. The position is still closed and Black is rather lucky it is "just" 1.0. Look at a few Morphy games to see how opening errors like these get punished mercilessly.

19880: <pre><code>[FEN &quot;rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR&quot;]
[Title &quot;Berlin Defense&quot;]
[StartFlipped &quot;1&quot;]

1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. O-O Bb4?!
</code></pre>
<p>When White castles, Stockfish evaluates the game to be roughly equal. After Black responds with <strong>Bb4</strong>, the evaluation goes to around <code>+1</code> and Stockfish labels it as an inaccuracy.</p>
<p>What is wrong with Black’s move? It leads to a more symmetrical position so I’m surprised that it’s considered bad.</p>
 11144: <p>Easy: The bishop not only shoots thin air, but also asks to be kicked around with c3, such that White wins a tempo with a move he likes to play anyway in Italian/Spanish positions to make a big center with d4. Thus, after c3 (immediately, or after Re1), White is simply a tempo up with respect to &quot;normal&quot; variants. The position is still closed and Black is rather lucky it is &quot;just&quot; 1.0. Look at a few Morphy games to see how opening errors like these get punished mercilessly.</p>
