为什么单膝跪地是求婚因为双膝跪地是上坟呀
[wéi shén me dān xī guì dì shì qiú hūn yīn wéi shuāng xī guì dì shì shàng fén yā]
Why kneeling on one knee is for proposing because kneeling on both knees is for mourning at graves. This humorous saying compares the postures used in proposal ceremonies versus funerals in China.