Never believe your own propaganda - you'll underestimate your enemy.
And the comeuppance can be fatal.
At first it's easy to make light of "slopes" in sandals made from old tires and living on rice. And believe you and your buddies are the meanest, toughest, best equipped, smartest SOBs to ever walk the face of the Earth. That cost the lives of many, many good people.
They had fantastic discipline, intelligence, determination and practice. Smarter than hell, they wouldn't attack a fixed base until they knew exactly where everything was.
And they'd probe, test, snoop, pry, have diversions, ambushes, traps. And weren't afraid to die.
Arf