盈：圓。虧：缺。月圓的時候就是月缺的時候。形容物極必反。
盈則必虧是一個漢語詞語，讀音是yíng zé bì kuī，是指形容物極必反。 更多→ 盈則必虧
When the fullest extent is reached, waxing is definitely followed by waning