The Zen of Python

In the Python shell try the following:

import this

You will be surprised with the result of the command above... the Zen of Python:

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

which is a set of guiding principles for Python's design, by Tim Peters, divided into 20 aphorisms, only 19 of which have been written down. I've posted this not only because it's an interesting curiosity but because I feel that these are almost always good principles to follow when programming/coding/hacking... let's keep them present in our lives...

But there is also a mystery here... what is the 20th, not written, aphorism? I've seen many jokes around this matter in the Internet but no credible answer... can someone en-light me on this?