From Bai Juyi's Tang-dynasty poem
《琵琶行》 (Song of the Pipa):
千呼万唤始出来,
犹抱琵琶半遮面 — 'after a thousand calls she finally emerged, still half-hiding her face behind her pipa'. One of the most famous lines in Tang poetry; the idiom evokes its reluctance-and-anticipation image.