As a famous line by the ancient philosopher Heraclitus has it, you cannot step into the same river twice. Even if you return to the same spot on the bank, different water flows in upon you at every moment. Similarly, to see the world exactly as you did half an hour ago is impossible, just as it is impossible to see it from the point of view of a different person standing next to you. The mind flows on and on, in a ceaseless ‘stream of consciousness’20 – a phrase coined by the psychologist William James in 1890, though it was later made more famous by novelists.
