[tabs_masterrace]

Yeah, I think chess can give you cold hard feedback on how well your mind is working on a given day. As the author already mentioned, performance can vary a lot. When you're doing poorly, you often don't feel very different, but then you sit down to play chess and realize you're basically sleep walking. What you're looking for is a fully awake, high alert, high awareness state of mind. Factors like diet and regular exercise can make a huge difference in my experience.

[will_pseudonym]

Absolutely. It is always a really indicator of if I'm tired or not if I start to fail a lot of chess puzzles where I should have seen something, but just didn't notice it because I was tired. As someone who tends to stay up late, it's been nice, because I have an objective measure of my cognitive decline from being tired that I wouldn't have seen otherwise, and it's made me want to go to bed so that I'm not tanking my puzzle rating on Lichess, haha. :)