If you're wondering why blackface -- mimicking people of African descent via stereotypes and makeup-darkened skin -- is a big deal, then perhaps a little history lesson can help demystify the outcry. Dwan Reece, curator at the National Museum of African American History and Culture, explains how this practice permeates the American psyche and culture (in theater, music, books and beyond) and why it's not simply harmless fun, but a legacy of oppression.