From Liu Yong's 《
蝶恋花·
伫倚危楼风细细》 (Northern Song), paired with
衣带渐宽终不悔.
伊 (yī) is a classical pronoun meaning 'she / that person'. Wang Guowei's 《
人间词话》 named this couplet the 'second realm of scholarship' — the stage of single-minded devotion to a pursuit.