In my experience, it's not tired/lazy/inattentive, but resignation. You normally have some expectation what students will be able to solve. Typically, these exp

In my experience, it's not tired/lazy/inattentive, but resignation. You normally have some expectation what students will be able to solve. Typically, these expectations are set too high. That's very common, not only for me, but for pretty much anyone I know. So over the time of grading, one adjusts down the expectations and gives partial credit earlier, for example.