How do mistakes contribute to self concept?
Your mistakes can make your self-concept stronger and more accurate. How you represent counter examples to a quality has a major impact on how you think of yourself and how you behave.
Having no counter examples makes the quality less real. It can also create an impossibly high standard, and make someone resistant to feedback. Denying imperfections leads to the shadow self and an all or nothing approach (I am either totally good or bad). Flipping from a positive to a negative database of examples is very common.
Having too many counter examples or ones that are too large or prominent on the other hand can weaken or overwhelm the other examples. 5-10%, in the same modality, mixed in with other examples is a good proportion. It is important not to have future counterexamples.
Changes to the scope of the quality can transform unuseful counterexamples and expand your resources. NLP Techniques such as Change Personal History and Time Line Therapy work well here.