Superstition is the irrational believe in supernatural circumstances, and typically those related to fair chance or bad luck, even when such circumstances cannot be explained with a natural phenomenon or rationally but it's still traditionally accepted and very popular.
So builder owners deliberately exclude or miss the 13th floor, generally due being considered of <em>"bad luck"</em>, mainly by religious people <em>(in Christianity Judas was the 13th disciple who betrayed Jesus)</em>.
