I have been playing on wbaduk and have yet again discovered what a mind game go is. I can win if I actually focus on the game. But if I have to play in a hurry or am distracted or annoyed by my opponent's unreasonable play, I do make stupid mistakes.
As in misreading something obvious or messing up a joseki I know well enough. Or suiciding while trying to kill my opponent. Very frustrating. And very clear that calmness of the mind has a huge influence on my go game. As it does on my life, but that is another story.