Psychology behind blunders
When I first started paying chess, I started from 5min blitz games; these fast games are, obviously, games where players commit blunders pretty frequently. I was one of those players, but the more I started to recognize a pattern behind my blunders, it eventually came to my attention that blunders are always resulted from a fixed subjective mindset.
Yet even though I commit less blunders now, I still commit them.
I'm still figuring out an on/off switch for a completely objective machine brain i.e. a fixed... you guessed it -- mindset.
1. Estimating yourself
For example: when a game's pattern reaches out of recognition, some players tend to get afraid and spend a huge amount of time calculating one's opponent's every potential aggressive line, while ignoring one's own most aggressive potential play.
Another example: some players tend to feel superior to one's opponent and won't value the importance of calculation as much and tend to quickly calculate one aggressive line for oneself, while ignoring the opponent's potential counter play.
Here's a game with a fast player, who managed to provoke me to play fast as well. He gained a good advantage by forking my queen and knight with a pawn. In this given situation, I started to value calculation and calculation only.
In the end, tables turned due to his lack of observation and calculation.
2. Emotions intervene logic
For example: trying to trap a piece or mating the king by a little too pure aggression. Sacrificing pieces to break a pawn chain etc. and going all in for the attack, only to notice it was premature and the opponent managed to survive or counterattack you.
Here's a game with an aggressive player. This player decided to go for a King's Gambit setup, even though I was responding with Caro Kann Defense. Is it just me or do you as well think that this player started feel something towards my Queen?
3. Perceptual blindness
For example: one creates or participates in a situation to fight for middle control and later on forks somewhere else, while still defending/pressuring/attacking wherever a situation is at hand. Some fall for perceptual blindness, which is caused by a subjective mindset that one should focus only on one positional area.
Here's an interesting Spanish game (Ruy Lopez), where my opponent kicked my bishop immediately away to feel more secure, only to roll a red carpet for my Queen later on.
4. Estimating your opponent
For example: one's opponent seems to be playing so well and embracing all kinds of tactics that one is prone to deny his opponents blunders.
Another example: one's opponent seems to be playing so poorly and missing all kinds of tactics that one is prone to deny his opponents potential.
Take note: he also fell for perceptual blindness, when he tried to skewer a pawn after missing my blunder.
Edit: no matter how counter intuitive it sounds, but estimation of oneself and one's opponent is a base for a blunder. The most logical move to a situation is always the most logical move, no matter if the player's ELO is <500 or >2500.
To embrace risk is to embrace potential blunders.