You know, this discussion got me thinking about the myth of Arachne: a mortal woman in the supposed mythic past of Greek Asia Minor* who wove perfect tapestries, and dared Athena herself to a weaving contest. When the costest was over, Athena admitted that Arachne's work was flawless, but its subject matter (Zeus's infidelities) was insulting to the gods.

In a rage, Athena destroyed the work and the loom. And Arachne hung herself out of shame. But the goddess took pity on her, after death, and brought her back to life in the form of a spider.

As far as I can recall, the tale does not end with a specific admonition that you should deliberately include a flaw into your weaving, in order to avoid Arachne's fate, but that's certainly a reasonable conclusion for the reader to make.

*Recorded in the works of Ovid and Virgil, but never appearing as a story on an actual Attic Vase. And after reading through this discussion, it seems that a) the idea of including imperfection to avoid Divine wrath is, indeed, very widespread, and that b) part of this belief is also that it originates with an older, more exotic, or wiser culture than our own (the Navajo, the Ancient Chinese, the Freemasons, or, for Ovid, the ancient people of Lydia) -- almost as if attributing the practice to "the Other" gives it extra authority.