Failure is probably the most fatiguing experience a person ever has. There is nothing more enervating than not succeeding being blocked, not moving ahead. It is a vicious circle.
Failure breeds fatigue, and the fatigue makes it harder to get to work, which compounds the failure.
In the former case, we keep putting off a task that we are under some compulsion to discharge. Either because it is too tedious or too difficult, we shirk it . And the longer we post pone it, the more tired we feel. Such start-up fatigue is very real, even if not actually physical, not something in our muscles and bones. The moment I find myself turning away from a job, or putting it under a pile of other things I have to do, I clear my desk of everything else and attack the objectionable item first.