Some fifty years ago, in the early 70s, I was in southern Italy for nearly 1½ years. I drove a car most of that time. I was far from any big city like Rome or Naples, but I was still terrified of driving there. The small towns were very crowded with very narrow streets, and drivers who raced around as if they all had a death wish.
It took me about half a year before I learned there was a method to their madness. The unspoken 'rules of the road' in Italy were quite different from anything I knew from driving in the USA. Once I finally got all that, I gained some respect for Italian drivers and lost most of my fear & loathing of driving there. But it took me half a year of terror before I got there. When I first returned home, I experienced the same terror that I had felt early on in Italy, while driving among American drivers.
I don't think a short visit to Paris, Bombay, or even Boston, is nearly enough time for anyone to unlearn his USA driving habits and start to understand completely different rules of the road.