A nation has borders or boundaries(边界) and everything within those borders belongs to that nation. Many a war has been fought over boundary disputes(纷争). So, too, people have private territory(领地); and Westerners take the concept(概念) of personal territory very seriously.
For example, both in homes and offices, desks and desk drawers are private territory. The letters, documents(文件), journals or even newspapers on top of the desk belong to the person whose desk it is (even if the desk itself is actually the private property of an institution). Without asking permission, we do not pick them up and read or look at them. The vast majority of people will gladly lend you what is theirs—just ask. By the way, it’s also impolite to read over someone’s shoulder.