女为悦己者容男为己悦者穷
[nǚ wéi yuè jĭ zhĕ róng nán wéi jĭ yuè zhĕ qióng]
The saying translates to 'A woman beautifies herself for one who finds joy in her; a man exhausts himself trying to please the one who brings him joy.' This speaks to human behavior driven by love and the pursuit of affection, especially concerning self-improvement for another.