This, explains Daisetsu T. Suzuki (1870-1966) in "Zen and Japanese Culture," is how Japan's most famous haiku came to be written:
Matsuo Basho (1644-94), samurai-born but a rootless wanderer most of his life, was a deep student of Zen. One day his Zen master Butcho paid him a visit at "home" — a "broken cottage" by the Sumida River in Edo (present-day Tokyo). "How are you getting on?" the master inquired.
"After the recent rain the moss has grown greener than ever," replied Basho.