I too have heard the story that Navajo weaving must have an imperfection in it. Don't know where I heard it, though.

Here's a related thing that have more validity. I once read a book about pottery from the pueblos near Albuquerque. (I think it was Albuquerque.) The book was a reprint, probably by Dover, of an original of about 1910.

At that time, the women of the pueblos made huge jars for storing water and food. The jars were very resonant, and the Indians thought there was a spirit in there that made the noise. When the women painted the lips of the jars, they left a little gap so as not to trap the spirit in the jar.

A person of today, seeing the little gap, might invoke the imperfection theory, but that would be wrong.