The struggle seems to go on forever. Sam has already fought, and won, his own battle. Dean, on the other hand, still hasn't managed to get the upper hand. From his position by the door, Sam is unwilling to help. He knows Dean won't appreciate it.
There are some things, Sam reflects, their father was completely negligent in teaching them. Skills Dean has obviously never made the time for.
Sam wonders, yet again, at his brother's prowess at hand to hand combat, martial arts and weaponry, amongst others things, whilst remaining totally incapable of putting a sheet on his bed.