Symbol and its meaning

There are things that we see everyday and we know what it means and what it stands for without being told. We associate a nation's flag as a sign of patriotism. We associate symbols to a meaning, in other words, we give symbols its meaning without realizing it. But how are we doing it and why would we do it to ourselves? The word "we" is rather vague as because it is use to generalize the entire population. Its rather a group of individual or an individual who wants to insert a meaning upon something. It is achieved by repeatedly showing the symbol with its definition either directly or indirectly by metaphors. For example, the flag is view as a sign of patriotism, how? Because at every government building, there is an American flag. When you enter a school, there is an American flag. In recent elections, pictures and television broadcast of candidate all show with an American flag in the background. The picture of the flag raising on Iwo Jima during World War II being use as propaganda to fuel war efforts. So when we, the general population, see or think of the American's flag, we associate it with government buildings, heroic victories of battles, democracy and etc. When you repeatedly show or assign a definition either directly or through metaphor with a symbol, it becomes that meaning.
-Thinh