We are humans and we make mistakes, this is normal. There are some typical cases in which chess players make the same mistake(s) repeatedly. In this lesson about defense, you will recognize and understand those mistakes. It will help you avoid those mistakes in your future games and it will drive you in cloud nine! 
Mistake #1 – Underestimating opponents’ threats
White to play
When we are playing a game, our opponent sits opposite to us and he/she wants to win as much as we want to. Don’t forget that we are not the only one playing the game, and what is more important we are not the only ones who are playing to win. Thus, we should pay attention to our opponent’s threats and we should ask ourselves: what does she/he have in mind?
Topalov who plays with the White pieces in the game above, played Nd2. This was the decisive mistake because after 35…dxc3 White has huge problems. Two connected passed pawns are very strong and Black managed to win the game afterwards. The game continued: 36.Nc4 Re8 37.Rxb7+ Qxb7 38.Qxe8 Qb1+ [38…Qb1+ 39.Qe1 c2–+] 0–1
Mistake #2 – Blunders
Black to play
A blunder is like a slipping on a banana peel. Sometimes, even the TOP grandmasters can make such terrible mistakes. It is not something they intend to do; it is simply a mistake, an error. After the blunder, the position immediately collapses.
Adams who plays with the Black pieces is forced to move his King. The correct reply is Ka7 in order to protect the Knight on b6. Instead, he played Ka8 and lost a piece after the forcing variation: 34.Rxd8+ Rxd8 35.Qf6
Black to play
This is a double attack to both the unprotected d8-rook and b6-knight. White won the game afterwards. 35…Nc4 36.Qxd8+ Ka7 37.Qd3 Nxb2 38.Qf5 Qa1+ 39.Kd2 Nc4+ 40.Ke2 Qxc3 41.Qxc5+ 1–0
Suggestion: You may like to read about “Two chess opening mistakes you should never make”Mistake #3 – Counting on your opponent to play not in the best way
Black to play
In the above game, Nakamura played the move 13.Ne2 very quickly. Perhaps he confuses his opening preparation or he just would like to confuse his opponent. Please let me remind you that he is one of the best blitz players in the world. Unfortunately, Blitz is very different from classical chess.
After the forcing variation: 13…Nxe4 14.Bxd8 Nxd2 15.Be7 Rf7 16.Bxc5 Nxf1 17.Rxf1 b6 18.Bb4 Ba6 we are getting to the following position:
White to play
White has strategically lost the position because the pawn on c4 is a very weak one and Black’s plan is very simple. Black will double his rooks on the c-file and they will capture the weak pawn. Black won the game easily.
Mistake #4 – Play without castling
Black to play
The most dangerous strategy is to leave your King in the center of the board, because the center usually can be opened easily. Thus, my advice is to castle as soon as possible and keep those pawns snug (f2,g2 and h2) right in front of your king.
Many chess players leave their King in the center for long time, and because of that they lose their games. I hope that you will not make this mistake and will secure your King.
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Karjakin beats Carlsen, in classical chess, only for the 
“I didn’t have time at all to calculate,” Karjakin said about the critical differences between 37…Qd3 and 37…Qa4. “Having one minute on the clock, it was impossible to understand.”
Carlsen was visibly uncomfortable (as seen above) and a few moments later, he got fed up and went away. He did not return to attend the press conference.
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