In some religious community, perhaps the Shakers, it was believed that only God could create something perfect. Hence creating a perfect object was considered trespassing in God's domain. So all crafts, from chairmaking to quilting to painting, had to include a perfect flaw. Of course, some flaws rendered the object unusable. So a secondary art form emerged, of creating a beautiful "flaw" inconsistent with the overall work, yet appealing in its own right.

example: The sweater I knit with one cable twisting in the opposite direction from the other cables.