"Walking on two banks of a stream is a laborious exercise. Rather frequently you see a man (a student of magic) going up-stream that way, walking on the one bank and the other at the same time: being very preoccupied, he does not see you. For what he is performing is delicate and tolerates no inattention. He would very soon find himself back on one bank, and how disgraceful that would be!"
• Henri Michaux