How to Convince a Flat Artist That the Earth Is Round

In order to convince a flat artist that the world is round you've got to make him act consistently on his own proposition. To find the edge of the world we must be very very careful that we don't go round in circles or we'll never get to the edge. In Zen when you finally convince the master that you are stupid enough to be accepted as a student because you persist and because you've defined yourself as someone having a problem he has warned you.