This is actually not a bad thread. I have just about given up on chess a couple of times. It gets pretty depressing when one throws away an easy win. Good advice. Check out my last game.
Being psychologically well prepared/Blunders due to nerves
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Some stuff I discovered that prevented me from losing my mind
Sharing is caring. I would also like to hear your thoughts and see game positions where you blundered due to nerves 
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Type of blunders that can occur due to psychology; not visualizing that a piece is at a new square, missing that take is with a check, missing a counter-threat, missing a candidate, missing a capture, only making pawn moves, not seeing a piece, tactic, missing a check.
Typical types of psychological reasons behind a blunder: confusion & frustration; advantage in the opening is gone, realized that putted too much risk in the opening, won position is gone, advantage/won position is gone and unable to evaluate this endgame, plan got ruined due to “imaginative” move/didn`t go as planned), overseen in calculation.
Lose of self-confidence: Lose of self-confidence means to believe that you are unable to improve much higher/”I suck at chess because I am talentless” and not being ok with that. That you suck can be true and can be not true. It`s possible to lose self-confidence during tournament and then there are two choices: to continue playing in the tournament or TO QUIT CHESS!
Anger: Blaming others: “This GM in his DVD recommends shitty openings that only bring me in trouble, “This is among top moves in the database, why the **** my position is equal/worst now???”
Often when there is enough time on the clock one can handle the frustration but if you step in time trouble and opponent is more active or has some initiative, even mortal initiative the confusion and frustration that your brain was toxicated with in the last couple of hours will most likely show effect if the player is not psychologically well prepared.
Be ready that sometimes or perhaps many times things will not go as you want but that is not because you are a moron but simply because your chess is not so perfect yet, just make the best of current position, don`t get frustrated and confused. This means being psychologically well prepared.