Well the truth is we forget the time tracking system too. The solution is to keep the system in your face.
Maybe a programming/assembly analogy can help you understand the issue.
In my case, ADHD makes my brain want to work in a parallel way.
While I'm busy with task A it's like HEY CONDSIDER TASK B. Did you see C?
On good days, we see that and say NO OP - BUSY WITH TASK A. And refocus our mind.
Say it's a bad day...
Instead of CONSIDER TASK B, it's more like GOTO TASK B. And here it's equally harmful.
What should happen is the registers (context) of the CPU (brain) should be saved when task A stops. Likewise before task B starts it should be fully loaded into the brain.
None of these things happen for us.
So task A is left in an unfinished state, the context to finish it dissolved into thin air. Task B is started without properly being prepared which negatively impacts efficiency and performance.
And the moment the going gets hard, dopamine release decreased, you can feel it coming...
INTTERUPT - GOTO TASK C.
So it's managing that that's hard. Writing things down helps a lot, but good luck remembering to write :D
Here's the thing: sometimes I forget the timer is running and I wake up to "You've been working on [project X] for 28 hours".
I just turned off my phone's voice recorder after 4 hours and 28 minutes. I needed the first 15 mins.