A dull knife is more dangerous than a sharp one because you have to force it. Same with a tired mind.

When the tool has lost its edge, you compensate with pressure, and pressure is what makes things slip. A tired mind does not simply produce less, it produces force where precision used to be, which is when careless mistakes and sharp words arrive. The danger is in pushing a blunt instrument.

When you notice yourself forcing the work, treat that as information rather than as a reason to try harder. Sleep, eat, or stop for the day and come back to it. Twenty minutes with an edge beats two hours of leaning on the thing.