People always need something to feel good about, and when you're one of those people that doesn't have a whole lot to be happy about otherwise, a bit of national pride can help you stay productive and motivated, and governments have certainly managed to use this sentiment quite effectively over the centuries. However, sort of like religious faith, it is sort of fundamentally bullshit at its core, which everyone more or less realizes but which we can't do anything about cause it's sometimes better to believe the comforting lie than face the harsh reality.