Once or twice [Joyce] dictated a bit of Finnegans Wake to Beckett, though dictation did not work very well for him; in the middle of one such session there was a knock at the door which Beckett didn't hear. Joyce said, `Come in,' and Beckett wrote it down. Afterwards he read back what he had written and Joyce said, `What's that "Come in"?' 'Yes, you said that,' said Beckett. Joyce thought for a moment, then said, `Let it stand.' He was quite willing to accept coincidence as his collaborator.
A beautiful sentiment that, coincidentally, goes some way towards explaining the incomprehensibility of Finnegans Wake.