平行线里没有相交垂直线里没有平行
[píng xíng xiàn lĭ méi yŏu xiāng jiāo chuí zhí xiàn lĭ méi yŏu píng xíng]
Parallel Lines Never Meet, Perpendicular Lines Have No Parallelism. It metaphorically suggests the incompatibility or distance between relationships which can never intersect or remain indifferent even when they try to be alike.