Mind is often likened to an ocean – a deep body of water full of immeasurable movement and mystery. And it is, of course, but it has become something of a sewer, or at least a smelly canal, polluted by all manner of detritus – plastic bottles, used condoms, motor oil – and all manner of shit that's sunk to the bottom – no longer visible but slowly fermenting, sending up occasional bubbles of noxious gas to remind us of the scale of the task ahead if we ever want clean natural water able to really sustain life and creativity.