Adaptive cruise control with stop and go can understand surrounding and knows when to stop and go. With that if I add paint path as this demo then self driving

Adaptive cruise control with stop and go can understand surrounding and knows when to stop and go. With that if I add paint path as this demo then self driving should work. But in reality it ain't. So There is something else which seems like too hard to solve problem with self driving . I want to know what is that