Just this: You’re riding the Bx 19 bus up 149th Street to the Grand Concourse. On your headphones, the mad Jewish carnival that is Masada, the song is “Karaim,” on the album Gimel, these words mean nothing to you, but the music still conjures images of acrobats somersaulting between trapezes and elephants stampeding around tents. And what should you see when you look out the window but a black man furiously pedaling a unicycle up the hill beside you, keeping pace with the heaving motor of the bus? This latter-day John Henry, a circus runaway, surely, first to, then from. He’s balanced high above the pavement, his coat is slung over one arm. Such serendipities can happen anywhere. But why do they seem to happen with such greater frequency in New York?