Depending on whom you ask, there are between 189 and 196 independent countries in the world. While they may share similarities, each has developed a unique culture with customs and pleasantries unlike anything else in the world. Just think of how many differences there are just between the states in the United States. Could you possibly confuse a Brooklynite with someone from Mobile? Adjust that paradigm to the whole world and you get an idea of how complex humanity has become.
Some customs develop because of the war history of a nation, or the style of a king from centuries ago. Other cultures develop customs based on superstitions, or legends, or the intersection of multiple religions. For example, The Netherlands has a lot of customs that owe to the influx of Jews several centuries ago, and Thailand has customs owing to its former status as a French colony. Even the United States has legacies of our colonial time, with the inheritance of British Common Law forming the basis of our system of jurisprudence.
So how well do you know the world? When you visit a country, do you bother to dig into the local customs, so you can know what it is like to be a local, or do you just take selfies and hop on the next leg of your trip? Could you identify these nations from one cultural fact?