When after the game Alekhine was asked how he could possibly blunder like that, his answer was pretty simple : "I just forgot about the Bishop". Forgot about the Bishop? Alekhine?? For God sake, the man set the world record by playing 32 blindfold games simultaneously and here he forgot about the Bishop??
I could give more examples like these, but the picture is pretty clear already. Sometimes blunders happen just because as they say 'to err is human'. This is the most difficult kind of blunders to fix, because they happen with no warning and without any visible reason. And while the strongest chess players commit such blunders once in a Blue Moon, the average club player suffers from them pretty frequently.
I remember a certain period of my chess life when this problem got out of control. I was about 11 years old and even though we didn't have ratings at that point, I would estimate my strength was around USCF1500-1600. But suddenly I started blundering in almost every single game. I tried everything I could, but the blunders kept coming. It was very depressing because I knew I was going to blunder, I focused at every single move and yet, in the end, I always found a way to blunder! Sometimes when my move was not a blunder per se, it was still a blunder! I remember one of my stupidest blunders. In the Sicilian Defense my opponent played a typical Sicilian move b7-b5 and I played some typical Sicilian move like Kh1.
Unfortunately, my opponent's move b7-b5 was a horrible blunder since his Nc6 lost protection of the b7 pawn and therefore I could just win his Knight for free by playing Nd4xc6!
I noticed my miss immediately after I executed my move. I almost cried during the game. I didn't know what to do with this problem since the typical advice "be focused" clearly didn't work. Salvation came from an unexpected source. When I was in a library, I was browsing through an old book for beginners (I don't even know why I grabbed that book since I wasn't a beginner already ). Suddenly I found an unusual advice.
The author ( I think it was an old Soviet Master Chekhover, or was it Panov? I don't remember) recommended a simple algorithm. Before you play any move ask yourself: If I play my intended move, what are the possible checks of my opponent? If you don't see dangerous checks, ask yourself "what are the dangerous captures of my opponent"? And then ask yourself if your opponent can threaten any of your pieces. This simple procedure will pretty much insure that you are not making a stupid blunder because in practically all the cases when you blunder it is either a check a capture or a threat. Also look at all available checks, captures and threats of your own, to make sure that you are not missing a blunder of your opponent (as I did in the above-mentioned game). Initially when I read this advice I thought that the author was insane. If I follow this algorithm every single move, then I'll run out of time by move 15 or something like this. But as I said, I was desperate, so I decided to give it a try.
At first I felt kind of awkward doing this, but with a little practice I noticed that the whole blunder-check would take no more then one minute per move. And you'd agree that one minute per move is not a big price to pay in order to avoid blunders. The most important thing is that I was cured! Of course, just like any human chess player I still blunder. But not in every single game! If the problem that I described here sounds pretty familiar to you, I recommend you to try this recipe of an old Soviet master whose name I forgot (shame on me!).
I sincerely hope that our six part discussion will help you to avoid blunders in your games and consequently improve your chess results.