It's not a perfect analogy, but I think it's very similar. Teachers have to interact with all students, not just the ones who have trouble, but the ones who have trouble occupy a greater portion of the attention of teachers. So teachers spend an inordinate amount of time dwelling on the matter of neglect and abuse. The saddest most depressing cases stay in the minds of teachers for a long time, while the normal well cared for students are soon forgotten.