I read an article about American social life and I have found a very interesting facts about the United States; that people do not use a term "must" frequently in their social life even though the term "must" is one of the most basic vacabularies that English learners face.
When American people advice their friends or the others they know, they do not use the term must or have to be. It is something that is cultural thing in United States, even though they advice to their friends about something, they do not force the others to do something because they believe the choice is the oppenent's freedom.
It is a very interesting article at least for me, because in South Korea, most of people advice to the others using the term "must" even though the people are not aware of the opponents if they are doing something wrong. American way to advice to the others might seem to be very kind, but I realised it that the advisor isn't 100% thinking for the opponent.