I see this a lot with students in introductory physics. If they come to me and say "I don't get it" or "I can't get started" I actually invest less time than if I get a good student who has hit a wall and can't get through. The student who won't/can't start will get sent to the tutoring center and I will spend the time with the kid who works hard. There's only so much of me to go around and I want to make it count.