A demolition man was tasked to take down an odd looking building

It was a ridiculous eye-sore, built with all kinds of materials and no roof above. 

On the first day, he goes over to the northern wall made entirely of cardboard. With a few easy swings of his sledgehammer, he brings it down. He returns home, without breaking a sweat.

On the next day, he goes to the eastern wall which is made entirely of thin sheets of metal. It takes him a while to knock it down. Just mildly exhausted, he goes home satisfied.

On the third day, he goes to the wall on the west, built with slats of solid wood. It was no easy task, although after a day of hard labour, he tears it down and goes home very exhausted.

On the fourth day, still exhausted from the previous days’ work, he finally goes over to the southern wall—6 inches thick, and made of reinforced concrete. It did not give in easily. After hours of constant striking, a small part broke off.

With not an ounce of strength left, he looks up at the sky and asks, “Is this some kind of a joke? I quit!” and throws his hammer and proceeds to walk away.

At which point a voice steps in - “Whoa! You can't do that. That wasn’t in the—”

“Hell yeah, I can”, he turns and snaps at the voice. “I just broke the fourth wall”