We're really only wired for 4-5 hours of deep, productive work each day. A lot of people try to push that to 7-8 hours and add more hours on top of that for other work-related tasks, not realizing the toll it takes on your energy and creativity in the long term. A crash is inevitable, and can appear in subtle ways (burnout is not always an explosive event).
Recognize those times when you're just not going to get it done, and either stop completely so you can go and rest and refresh. Or, if you are required to still be "on the clock" for some more hours, do low effort, reactive work as much as possible.
Example - Part of my work is producing video training courses. My workflow fits into the limitations I've identified in myself. If I need 10-12 hours to write the script (what I'm going to say) for a module and create the slide deck (diagrams etc you'll see on screen), I'll break that up over 2-3 days. When my creative energy to write the material is drained each day, I switch to another task like recording audio for previously written modules (physically draining), then switch again to a low energy task like editing (boring but not mentally or physically taxing).
You are right @Cunningham, people fail to realize that we only do deep work for 4-5 hours.
If this happens after your deep work time, it's better to call it a day or to do low effort work as you said.
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