In OTB games I suffered incredible tunnel vision. It was two things really, firstly I just wasn't experienced enough, and though I shouldn't have been making blunders (I was playing some fantastic games with really well thought-out endgames) I wasn't calculating deeply enough in some situations and just making automatic moves. The other problem was that I was too nervous, and because of the first point, I'd end up not seeing an opponent's move (especially at lower levels where it's more unpredictable) and fail because of it. I fixed the first one by playing lots of games at once on here and spending daily time on tactics trainer and doing puzzles on a real board at home, and I solved the second one by actually forcing myself into a routine before I made my move - the first part was to check my clock to make sure I had time to ponder the position, the last part was to double check my candidate move to make totally sure it wasn't a blunder. This didn't necessarily work out the first few times (I still slipped into automatic occasionally), but once I managed to calm myself down (nicotine played a large part in this) I found it a lot easier to follow my routine each move (that needed calculation, by that, if I worked out a series of moves that were forced, for example, there's no need to work out the other moves) and it really helped.
I also find that analysing my games afterwards has helped a hell of a lot, and running through masters games has really helped instill more confidence in me of which moves to start looking at. Just sitting down in front of a board and running through what I did. It also helps with self-confidence, I played a game where I ended up with an advanced pawn on the d-file, but my opponent was busy defending it with rooks and a queen. There was a really straight-forward exchange I forced, which all of a sudden allowed me to move the d-pawn to the c-file and advance my b-pawn, completely changing the nature of the attack. Looking at it after the game, this exchange was undoubtedly the key to the whole game at the time, and I couldn't find another move that would give me an advantage. When you get it right, it's a great boost, and when you get it wrong, you can only learn from it.
I recently played a game in which I made the most inexplicable blunder.
I had picked up a bishop via a petite combination and was looking for the best way to consolidate my advantage. My opponent was trying to make up for his material deficit via a lame kingside attack with only his queen and knight - an attack that I (correctly) judged to be harmless. But it was at this moment my opponent played his queen to my d2 square attacking my Bishop on d3 with his queen and my pawn on f2 with his queen and his knight on g4.
This move came as a shock, and I spent at least a couple of minutes looking at the position trying to figure out what my best reply was and how I could possibly save both the pawn and bishop. What I was missing the whole time was that I could simply take his queen since I had a knight on f3!- I ended up playing my Bishop to e4, and I only realized my blunder after the game when I was running it through the computer and was startled to see the evaluation jump more than 1000 centipawns after his queen move.
Can you share your own stories of chess blindness and what you've done to fix the problem?