Okay, this wisdom comes from many struggles at the loom!!
Many times, mistakes that are made are ones that are simple oversights, that sometimes cascade into huge problems. But when finding myself in this situation, I like to remind myself that, even in the midst of this huge problem, I should not regret the place that I am in. A great deal of knowledge is gained by any mistakes or oversight. If nothing else, the mistake leaves such an impression as to remind you at every turn not to do that again! So really, mistakes are opportunities to help one remember how to do things correctly.
That being said, even when I remind myself of my good fortune to learn during my numerous 'opportunities', I still get frustrated!