I never made the link with the sound levels before. I just figured this out recently too. >6pm when people left the office and >8pm when the dull humming of t

I never made the link with the sound levels before. I just figured this out recently too. >6pm when people left the office and >8pm when the dull humming of the HVAC turned off gave this odd feeling of calm like it had been subconsciously aggravating me for hours. Also stumbled on a wiki article on "Directed Attention Fatigue" [1] which implied that the brain's way of focusing is not like turning up the heat on a laser, but more like applying multiple blinders to a horse to create a tiny reticle of focus. That basically meant clear out as many visual-field and sound distractions as possible to minimize the energy required for attention (and increase stamina, too). One thing I also try w/ the noise-cancelling headphones is only wear them during productive work, so that my brain subconsciously associates headphones on = work time. [1] https://en.wikipedia.org/wiki/Directed_attention_fatigue https://en.wikipedia.org/wiki/Directed_attention_fatigue