I used to design PID process controllers in industry. In watching this vid I realized one reason that designing a self-driving car is so difficult. Toward the end, in the process control diagram, he has [Vehicle] as the controlled process. This reminds me of the old math joke about "assume a spherical cow". The difficulty with a self-driving car is that it isn't just the vehicle that has to be controlled but [Vehicle + Current Road] so the controlled process is not just difficult to model but that it is changing all the time and sometimes rapidly.
