When a poker player thinks for a long time, he often makes a mistake. The phenomenon is so common that it has been reduced to a maxim: thing long, thing wrong.
While poker could be accused of having an anti-intellectual atmosphere — some poker players are opposed to thinking, long, short, or otherwise — chess couldn’t really; but even chess players notice a correlation between a long think and a blunder.
It’s easy to tell a story about why this happens: when you think for a long time you become entangled in irrelevant complexities, confuse yourself, and ignore your initial instincts. It would seem to follow that you can improve your performance by forcing yourself to play faster.
This all assumes that the long think is causing the mistake. There’s little doubt that in chess and poker there’s a correlation between thinking for a long time and making a mistake, but, as nerds are constantly reminding us, correlation is not causation. When two things are correlated, either one could be causing the other. In this case though it seems impossible for the mistake to cause the delay, because the mistake happens afterwards; so it must be the delay causing the mistake. But there’s a third possibility that’s often forgotten, that something else causes both of them.
Once you remember that possibility, it’s pretty obvious what’s going on. Not knowing the best play causes both delays, because you’re trying to figure it out, and mistakes, because you still don’t know what to do. While thinking for a long time and making a mistake are correlated, you probably can’t improve your performance by forcing yourself to play faster. What’s really causing the mistake is not knowing the right approach in a certain situation, and playing faster won’t help that. If you want to improve your performance, you need to become more skillful so that the situations where you don’t know what to do come up less often.