The most difficult part of my transition to life in France was the complete absence of online delivery. I practically lived off seamless in New York. When I moved to France I had to learn to cook for myself (!) and plan ahead to buy groceries (!!) since supermarkets are closed on Sundays (or only open until noon and, let's face it, I was most likely still in bed) and there aren't 24 hour bodegas on every corner.
In the US, there's such a focus on progress and innovation. Everything is meant to be efficient and fast. People are in a hurry and always busy. In France, it's kind of the opposite. The mentality here is more, "if it's not broken, don't fix it." This is changing a bit now but France is still a country very set in its ways, more likely to look back to its traditions and history than forward to its future.
Life is slower in France. Mealtime is very important and it would be considered rude for a server to drop a check on a table before being asked (it implies they are rushing you and trying to get you to leave). Coffee to go, while now a thing in Paris, is still a relatively new concept. Thanks to expats, we now have excellent coffee shops in Paris but in general coffee in France is an espresso at a café comptoir or on a terrasse, sipped leisurely while reading the newspaper or people watching.
Now I do everything more slowly than I used to. I stroll instead of speed walk. I spend at least two hours at a restaurant for dinner and usually closer to three (or four!). I sit on benches, look into windows, gaze at the sky. Living abroad has been an exercise in patience.