One of the deadliest chess sins must surely be materialism. In being blinded by something you can count, I had failed to see alternatives in my daily tactical training.
Take the following example I was trying to solve from Blokh's "Combinational Motives"
Can you solve the following?
Diagram 783: Difficulty 4, Black to Move
I had instead noticed the Knight fork at e4 and was attracted to 1. ... Qf2+ 2. Kxf2 Nxe4 3. Kg1 Nxc3 where I stopped my calculation, assessing that Black kept his extra Knight and was better.
I had made a number of instructive calculation mistakes in this analysis
Mistake: I had assumed White must capture my Queen
After 1. ... Qf2+, White is not obliged to capture the Black Queen but simply can play 2. Kh1. This is often a danger I have in calculation where I assume my opponent will cooperate with me ... that they are forced to accept my sacrifices, which explains why zwischenzugs often bring me undone
Mistake: Incorrect assessment, stopping half a move short
Whilst I had assessed Black to be better based on the extra Knight (materialism), I didn't appreciate the strength of the advanced connected passed c- and d- pawns after 4. d6. I has assessed incorrectly as I stopped half a move short in my calculation and not appreciated the opponent's strengths
Mistake: Playing for a win when not better
I wouldn't have considered ... Rxc7 as I didn't correctly sense that Black is actually fighting for a draw. This ties back to a bias that material outweights White's connected passed pawns.