wàng     méi     zhǐ       kě

  望         梅        止         渴

       The original meaning is that plum is sour and people who want to eat will salivate, thus quenching thirst. It metaphors that people comfort themselves when wish cannot be realized.

eg.他没钱买别墅，只好天天看着房屋广告望梅止渴了

      He didn’t have the money to buy a villa, so he had to watch the house advertisement every day.