user32408: I sometimes commit strange and embarrassing blunders when I fail to notice that my opponent's move has changed the nature of the position.  For example, recently I was playing White with the following winning position:
r1b1q1r1/p1Qn2k1/2pB3p/3pN1p1/3P4/4P3/P4PPP/RR4K1 w - - 0 24

After seven seconds of thought, I played 24.Qxc6, and my opponent responded 24...Nb6.  I am mortified to say that after 13 more seconds of thought (if that's the word for it) I played 25.Qxa8?? (missing a nice win with 25.Rxb6, but every reasonable move wins).
I suppose the psychology behind my idiotic error was based on some sort of residual memory that (a) the rook on a8 was once undefended, and (b) the knight on d7 was once pinned.  Am I the only person who experiences such catastrophic oversights?

user17425: This is a standard and common type of mistake.  It can take this form of not realizing the impact of the move made.  Another form is when you think you are still protecting something even after you move your piece away.
The final step before I move is always safety check.  Spend a few seconds asking whether the move is safe.  This help me a lot but I still make these error sometimes alas.

32408: <p>I sometimes commit strange and embarrassing blunders when I fail to notice that my opponent's move has changed the nature of the position.  For example, recently I was playing White with the following winning position:</p>
<pre><code>r1b1q1r1/p1Qn2k1/2pB3p/3pN1p1/3P4/4P3/P4PPP/RR4K1 w - - 0 24
</code></pre>
<p>After seven seconds of thought, I played 24.Qxc6, and my opponent responded 24...Nb6.  I am mortified to say that after 13 more seconds of thought (if that's the word for it) I played 25.Qxa8?? (missing a nice win with 25.Rxb6, but every reasonable move wins).</p>
<p>I suppose the psychology behind my idiotic error was based on some sort of residual memory that (a) the rook on a8 was once undefended, and (b) the knight on d7 was once pinned.  Am I the only person who experiences such catastrophic oversights?</p>
 17425: <p>This is a standard and common type of mistake.  It can take this form of not realizing the impact of the move made.  Another form is when you think you are still protecting something even after you move your piece away.</p>
<p>The final step before I move is always safety check.  Spend a few seconds asking whether the move is safe.  This help me a lot but I still make these error sometimes alas.</p>
