user21403: I am a total newbie in chess. I was playing with an ~intermidiate computer~ as White and made a pretty stupid mistake by playing Bf4. I waved the bishop goodbye, yet Black's rook did not capture it. Was there any good reason for the Black not to? The white pawns are moving downwards here. As far as I know, the pawn cannot move back to capture, so I reckon the bishop to have been 100% unprotected.
[FEN "8/4R3/8/4P1B1/6k1/PBP5/1P3r2/1KN5 w - - 0 1"]

1. Bf4 Rf3


user4418: Because the bishop is protected by the pawn -
[fen "5NK/2r3P/5PBP/8/1B1P/1k/3R/8 w - - 0 0"]

1. Bc5 Rxc5 2. dxc5

Not that it makes any difference. Black's position is hopeless.

user23782: When a "total newbie" achieves such an overwhelming position against a computer, it most probably means that the computer was forced to make a "sub-optimal" move from time to time - to give the player a chance to win the game. The problem is that the computer has no clue what is a "reasonable" mistake from a human point of view.
"Rxf4" might have been the best choice (not avoiding defeat eventually). But the computer decided not to make the best move, since the programmers told him to do so. In this particular case, this resulted in choosing the second(?) best move, which from our human perspective is absolutely incomprehensible.

21403: <p>I am a total newbie in chess. I was playing with an <a href="https://www.chess.com/play/computer" rel="nofollow noreferrer"><em>~intermidiate computer~</em></a> as White and made a pretty stupid mistake by playing Bf4. I waved the bishop goodbye, yet Black's rook did not capture it. Was there any good reason for the Black not to? The white pawns are moving downwards here. As far as I know, the pawn cannot move back to capture, so I reckon the bishop to have been 100% unprotected.</p>
<pre><code>[FEN &quot;8/4R3/8/4P1B1/6k1/PBP5/1P3r2/1KN5 w - - 0 1&quot;]

1. Bf4 Rf3
</code></pre>
 4418: <p>Because the bishop is protected by the pawn -</p>
<pre><code>[fen &quot;5NK/2r3P/5PBP/8/1B1P/1k/3R/8 w - - 0 0&quot;]

1. Bc5 Rxc5 2. dxc5
</code></pre>
<p>Not that it makes any difference. Black's position is hopeless.</p>
 23782: <p>When a &quot;total newbie&quot; achieves such an overwhelming position against a computer, it most probably means that the computer was forced to make a &quot;sub-optimal&quot; move from time to time - to give the player a chance to win the game. The problem is that the computer has no clue what is a &quot;reasonable&quot; mistake from a human point of view.</p>
<p>&quot;Rxf4&quot; might have been the best choice (not avoiding defeat eventually). But the computer decided not to make the best move, since the programmers told him to do so. In this particular case, this resulted in choosing the second(?) best move, which from our human perspective is absolutely incomprehensible.</p>
