The phrase ‘castles in the sky’ refers to dreams, plans, or ideas that are unrealistic or unlikely to happen. It is often used to describe ambitious but impractical goals or visions. The term originates from the idea of building castles in the air, which is impossible because castles are heavy structures that need a solid foundation on the ground.
In everyday usage, when someone says you are building ‘castles in the sky,’ they mean that your plans or dreams are not grounded in reality. It’s a way of suggesting that you should focus on more achievable goals. However, the phrase can also be used in a positive sense to encourage creativity and imagination, even if the ideas seem far-fetched at first.