Medical students who are planning their future may not have had enough time to think about what to have for lunch let alone the field of medicine they are going into.  In fact some interns may not know what field they want to go into until they are in the middle of it.  Those who choose emergency doctor jobs may choose them after they have had a rotation in the emergency department of a hospital.  Even once a doctor has chosen this field of medicine to practice in at first this does not mean that this will be the only field of medicine they practice or the only department they practice medicine in.