Here is a list of reasons why people lose at chess:
2006 is what he said; I thought he was talking about the year, not his rating adjourned move missing; I forgot to put it in the envelope and left it on table after the game, I noticed my opponent had two bishops of the same color as Black, forgot which way the pawns were moving in the endgame attempted to checkmate, but blocked by one of opponent's pawns, which was hidden from view behind his queen! Chair was too short to see over the pieces (contributed by Daniel McCandless) backward pawns bad bishop or bad bishops (locked in) bad move in a bad position bank rank mate was overlooked beans and bananas for breakfast boss came in while you were playing on the Internet at work castled into it check was overlooked checkmate threat was overlooked confused MCO column 12, note 6 with column 21, note 9 and lost queen counterplay was overlooked created holes developed my pieces too slowly or not at all diarrhea during the end game doubled pawns drawn game repeatedly declined by my opponent at least a dozen times endgame ruined my superior opening preparation endgame technique is weak en passant move was forgotten everyone watching my game agreed I was winning except my opponent exposed king faulty exchange forgot to say "J'adoube" and lost Queen while adjusting it forgot to stop clock while looking for the TD to ask what the time control was full moon glass chess set pieces opponent brought looked the same, lost Queen got too fancy greed hallucinated or ghost affect heart attack or stroke hypnotized by opponent and a spectator named Dr. Zukar I was winning on time until my opponent checkmated me knocked king over while I tried to shake my opponent's hand in a draw offer long diagonal threat was overlooked lost on time while I considered my opponent's draw offer lucky checkmate my opponent found before I could checkmate him mishandled pieces missed opportunity neglect of center noise opening preparation poor opponent did not follow my opening preparation that led to mate opponent had beaten a master the round before - with an iron bar opponent had no bra and bent over the pieces too much opponent sneezed on the chess set; said he had a contagious disease or bird flu opponent spent too much time in the book stalls during the opening opponent would not resign when he was in a lost position opposition of kings by my opponent perpetual check didn't last very long to avoid the 50 move rule played the King's Gambit Accepted and lost a pawn early on move two poison pawn or piece was grabbed positional errors queen and king looked too much alike in this East European chess set; lost Queen removed a defender and dropped a piece right moves were made, but not in the right order rook sacrifice failed when he took my Queen instead sacrifice overlooked sacrificed a piece, but then forgot why stalemate avoided stopped analysis one move short studied How to Beat Bobby Fischer and was unprepared for other opppnents sunglasses by my opponent blinded me from the glare tactical error; faulty tactics team captain said a draw was no good for the team, so I resigned tempo loss theoretical draw doesn't work in practice thought rook and pawn ending was a draw; he had the rook and I had the pawn time control must have changed; thought it was 40 moves in 5 hours, not 40 in 2 time pressure by my opponent; too much distraction watching the flag rise toilet break was too long; shouldn't have eaten 4 burritos and tacos at once transposed opening moves tried for too much uncoordinated pieces underestimated my opponent unjustified attack unlucky pairing with Walter Browne; played blitz chess and lost weakened castled King's position went out for a walk in the fresh air, forgot about tournament, kept walking wrong rook zugzwanged my opponent, but then he found a way out