I deal with a large number of people who are highly trained and didn't get a clear understanding of their subject. Most of these people did it by fixating on grades. I've had recent confessions of exactly that.
They have either picked something that they had no business going into or are going about it wrong. Either way shows poor judgement. I suggest more attention to the basics.
I've seen enough instances of this to suggest that a person look into the psychology of the matter. That does not say that the person has any mental problems.
Stacy:
In your instance, picking a subject far afield from the rest of your curriculum frequently results in depressed scores. You opened the door on "obsession" by saying that maybe you do obsess with grades.
I believe you are in the process of a healthy soul-searching. I hope you achieve a good balance between grades and understanding.
"Dropping back" to UNDERSTAND what you are doing may result in decent or even excellent grades with a reduction in effort!!! You may also discover that this excursion into another field doesn't warrant so much effort or worry.
BTW, Physics is exactly what I deal in. It eats the unprepared strangers for breakfast.
Mustang