The intentional error as an expression of humility is considered a way to honor the Great Spirit and to acknowledge being human. Ron Garnanez is a Navajo rug weaver who learned the art from his grandparents. "The traditional teaching of the Navajo weaving is that you have to put a mistake there. It must be done because only the Creator is perfect. We're not perfect so we don't make a perfect rug."
Other tribes see the mistake as a portal. In beading, the intentional mistake is called the 'spirit bead' and is believed to be the gateway through which the Great Spirit can enter the art. Some tribes attribute the error as a way for evil spirits to exit the design. There are those who believe that if you don't include a flaw in your woven blanket to let the evil out you may experience a form of 'blanket sickness'. Modern interpretation of this illness might include obsessive striving for perfect, the grandiosity of an inflated ego, or a lack of self esteem due to self judgement when you do make a mistake (a form of reverse grandiosity).... all of which tend to isolate you from other people.
It is not just Native Americans who include the practice of purposeful imperfection in their art. Persian rug weavers and Amish quilt makers are two other groups who employ similar policies in their craft. In addition to the expression of humility and honor, Persian rug weavers believe that mistakes also allow them to be more productive as they do not slow down their progress with needless worry, and that such freedom allows them to continually improve their skill. They support the paradox that that practicing imperfection can allow you closer to perfection.
So instead of automatically feeling bad the next time you make a mistake, think about another choice of perspective. Consider that mistakes are how we learn and improve. They keep ego from getting out of balance and help us see the world as it is. They provide us a means to acknowledge our humanness and to honor our higher power. Mistakes help us accept ourselves and others for who we really are, and allow us to love anyway.