A sloped roof is the worst possible place to try and balance a ball on; of course, it will slide off to the one side or the other.
However, the Impossible Rooftop by Kokichi Sugihara is, quite simply, impossible!
A ball placed atop the Impossible Rooftop will deny all the principles of Physics and stays put.
The Impossible Rooftop by Kokichi Sugihara won second prize in the 12th Best Illusion of the Year Contest 2015.
It is an optical illusion. The roof actually slops down in the center and the balls are “falling” to the low point. Clever, but hardly genius.