Why did you quit your job as a doctor?

Mama yang and big daddy go for the first big school conference when beano is in kindergarden. We are given all the test results, told that beano should probably be held back at the end of the year and then big daddy is presented with the question. Why did you quit your job as a doctor to go to work for the railroad?(says Ms. Smith). Huh? will have to ask beano about that one. Evidently beano has seen the picture from when he was born and had seen dad in scrubs and assumed that dad had been a doctor in his earlier life but loved the railroad so much that he quit to be a railroader. What happens when you assume?