Card Castle

Have you ever tried to make a castle out of ordinary playing cards, but they just seem to fall down all the time? It's hard for some people to simply stack two base cards, to form a triangle.
I found that making a card castle is surprisingly similar to physics. Stacking the cards on a tile floor is much harder then on a carpet because there is less static friction, and the cards slip too easily.
Also, in order two stacked cards to overcome gravity, they need to have equal and opposite forces on each other. And to do that, they need to have the same angle from the horizontal, but facing each other.
Then my card castle went higher then it ever did before. I was so happy that I named it Castel's Physics Castle!