They are shocked to find out that not all ambulances (in my area) respond to 911 calls.
Then when I talk to people about what interfacility transport is or transport decisions, they are shocked to find out that a lot of hospitals can't fully treat the patient or are not well equipped and staffed to do so. I think a lot of people imagine that you can walk into any hospital with any problem and they'll be able to resolve it there.
They are shocked that there are different types of ambulances: BLS, ILS, ALS, NICU/PICU. Especially in interfacility transfers, they can be frustrated when a BLS crew is sent to a call that requires an ambulance that is more capable to transport the patient. Sometimes they (the patient, the patient's family, and/or hospital staff including the register nurse) are upset because an ambulance is already here and do not understand why they have to wait for another ambulance.
People already mentioned minimal training, low pay, and poor working conditions too.