Really? You choose to enter the cave, even though you don't have any weapon, any armor, or any protection whatsoever? Why would you do this? To prove you're brave? You think this will impress the princess? Whatever, it's your funeral. I'm just following orders.
You walk into the pitch black cave, smacking your forehead that you forgot a torch, flashlight or any way to illuminate your path. Miraculously, you reach the dragon's lair with only minor cuts and bruises. You hear its lumbered breathing and can feel the heat of its smoke on your neck.
You charge at the dragon with...your bare hands. You slap its belly fruitlessly. It opens one eye, snorts out a fireball that chars you to a crisp, and bites off your head. You're dead. Big surprise.
Oh, and the princess? She liked you for your personality, not your bravery. Better luck next time, chump.