How ludicrous it would be for a dentist to tell a person with a toothache that he couldn't help him or for a lawyer to tell a person accused of a crime that he only took cases that had nothing to do with a crime or for a doctor to declare that he doesn't want any patients who are sick. That is what professionals do--deal with the problems people are facing. Yet, too many teachers demand that they only want students who are ready to learn--students without any problems.
Effective teachers believe and accept that problems of students will always be part of a teacher's job. They see problems as part of their normal, expected workload. They are not too hasty in wanting to pass off a student problem to the principal, the school psychologist/social worker, and/or to the Special Education teacher expecting them to resolve the problem.