We can know everything if we try. With the help of a variety of mass media, especially internet, we can search anything we want. That means that the world becames narrower,and there is no barriers of information or even the states. So we sometimes delude ourselves that we know evetything, at least, we are able to get to everything. Actually I didn't know before that we are careful not to thumb up to others. We usually show that when we mean 'You did a good job!'. But it means in Islam states that I despise you.
In modern times, the differences between the nations and cultures became diminished. But there might remain the tricky differences between them. Most of all, those culures and traditions must be respected however they seem to be strange to me or us. That's why we always be cautious to treat others and be careful to face the other's culture or customs.
* The image above was from clker.com.