Second, Carlsen is demonstrating one of his most feared qualities, namely his “nettlesomeness,” to use a term coined for this purpose by Ken Regan. Using computer analysis, you can measure which players do the most to cause their opponents to make mistakes. Carlsen has the highest nettlesomeness score by this metric, because his creative moves pressure the other player and open up a lot of room for mistakes. In contrast, a player such as Kramnik plays a high percentage of very accurate moves, and of course he is very strong, but those moves are in some way calmer and they are less likely to induce mistakes in response.

The match between Anand and Topalov was hard fought, partly because Topalov invoked a rule for the contest that forbids the players from offering draws to each other. The rule, named after the city where the match was being played, insured that there would be no short draws. As the match wore on and fatigue took a toll, both players began to make mistakes with greater frequency.