impossibility

• Ask for the moon

  To request something that is impossible or extremely difficult to obtain and therefore unrealistic.

• Promise the moon

  To make a grand, often unrealistic or impossible, promise that one cannot genuinely deliver.

• Not a hope in hell

  This phrase signifies that there is absolutely no possibility or chance of something happening.

• No chance in hell

  This phrase is an emphatic way of stating that something is utterly impossible or extremely unlikely to happen.