Just about every nation's military needs to perpetuate a mythos of invincibility. If the enemy believes even a little that your soldiers are better they are more likely to capitulate without armed conflict, or surrender more quickly. Similarly you own troops are more likely to fight and not surrender if they believe that their side is imbued with something that makes them better than the enemy. This has been basic PSYOP since the army of Uggg the Hairy convinced the army of Grunt the Cave Dweller that their spear-men could single-handedly defeat a dozen club men.

I'm sure that the North Koreans have an entire collection of songs, movies, books and stories about how their poor and rag-tag army drove the rich and well armed US army down south of the 38th parallel in 1950. I'm sure their version is that their people are braver, better trained, and guided by God (or a Kim, in this case).
Another example is Israel. When I hear astounding stories of how the Mosad executed some miraculous mission that would make James Bond shake with envy, I take it with a granary of salt, knowing that the only purpose of sharing operational mission info is to psych out your opponents and psych up your people.

As important as these PSYOP propaganda pieces are to maintaining military strength, they can be a double edged sword. They can lull a nation into complacency - making them believe that they are large and in charge because their people are somehow better and braver, their strategies and tactics are smarter and their technology and armament is better. Consider the the French in 1940. The Chinese Empire in 1270's. The Carthaginians in 200 BC.