I play a lot of chess and definitely notice a lot of day-to-day variation in how well I play. For me, the main factor seems to be if I had to wake up early or not. On days where I woke up naturally, I can pretty easily calculate out five or so moves, but on days where I had to wake up before the sun came up, it's much harder, and I can only clearly see two or three moves ahead. Caffeine seems not to affect this much.
I play a lot of chess and definitely notice a lot of day-to-day variation in how well I play. For me, the main factor seems to be if I had to wake up early or not. On days where I woke up naturally, I can pretty easily calculate out five or so moves, but on days where I had to wake up before the sun came up, it's much harder, and I can only clearly see two or three moves ahead. Caffeine seems not to affect this much.