Invisible Cities I --- Italo Calvino

Marco enters a city; he sees someone in a square living a life or an instant that could be his; he could now be in that man's place, if he had stopped in time, long ago; or if, long ago, at a crossroad, instead of taking one road he had taken the opposite one, and after long wandering he had come to be in the place of that man in that square.
By now, from that real or hypothetical past of his, he is excluded; he cannot stop; he must go on to another city, where another of his past awaits him [...].