In my opinion, when someone is doing a particularly hard physics (or other) problem, they go through 5 stages.
First is Denial. They will reread the question again and again in the hope that it will magically become easier. However, this is unlikely to happen so they move onto the next stage...
...Annoyance. Common thoughts and exclamations include 'You've got to be kidding me!' and 'Why professor/textbook/teacher, why?'.
The third stage is Procrastination. This stage is usually bypassed if the question is due next period. Otherwise it may continue for weeks on end until the person is forced past it by the threat of a deadline.
The fourth stage is Intimidation and Discouragement. The person is considering doing the question and is scared or discouraged at the momentousness and difficulty of the task.
And last but not least is Acceptance. This is where the person starts doing the problem for real. They've accepted that it's hard but will try anyway, even if they end up failing. In the case of REALLY hard questions, this stage will not be reached until the last possible moment, unless the person has an unusually good work ethic (I don't).