The poem teaches us that it's important to be realistic about our goals and expectations, and to accept the world as it is, not as we wish it could be. It's also important to remember that even in the midst of difficult times, there is always beauty and hope to be found.
Here are some specific examples of the moral lesson in "Air Castle":
* The speaker builds an "air castle" in their mind, a perfect world where everything is beautiful and nothing can go wrong. This castle is ultimately just an illusion, and when the speaker comes back to reality, they are left feeling disappointed and disillusioned.
* The poem teaches us that it's important to be realistic about our goals and expectations, and to accept the world as it is, not as we wish it could be.
* It's also important to remember that even in the midst of difficult times, there is always beauty and hope to be found.