One birdie lived in a cage, which was so beautiful and comfortable, she was fed there and she did't know another life.
Once the owner put the cage right next to the window, then this bird saw for the first time other birds that were free, they flew everywhere, their firsts developed in the wind and the sun's rays illuminated their smoothness.
They were so happy and free. The bird in the cage became very sad, because she did't know that it could be otherwise.