It refers to wishful thinking or unrealistic aspirations. This is used to describe someone who cherish foolish and exaggerated ideas. Example: John has neither experience nor qualification, yet he wants to be the director of the team? This is such a toad wishing to eat swan meat!
殺雞取卵 – Killing a chicken for an egg
It means the loss outweighs the gain; Fail to realise long-term loss for only a short-term gain.
白紙黑字 – White paper, Black Characters
It means somethings that has already been confirmed and cannot be changed anymore. Example: The contract has been signed by both parties. White paper, black characters, you have no chance to renege.