"Tokusan suddenly experienced great enlightenment."
One often reads bare statements like this in the old Zen texts. Sometimes it's only, "At these words, he experienced a deep realization."
What is being described?
Once upon a time in China, nobody wanted to hear anyone make grand or minor statements about Zen unless a Master had already publicly attested to that person's "enlightenment."
Yet the public seal of approval can't be confused with "enlightenment" itself, which is an experience only the person who is enlightened has.
There are some strange characters who pop up in Zen stories who are said by certified Masters to be "enlightened" but have no certification and are not monks -- an old woman who owns a tea shop, a father and son who roam the mountains as charcoal makers and, when asked a question about Zen, roar like tigers.