From Xiao Tong's preface to Tao Yuanming's collected works (
萧统《
陶渊明集序》, 6th c.):
白璧微瑕,
惟在《
闲情》
一赋 — 'a slight flaw on white jade, only in [his rhapsody] On Idle Feelings'. Xiao Tong was praising Tao Yuanming overall while gently faulting one piece. The phrase has carried that meaning — 'almost perfect, with one small flaw' — ever since.