In "The Wild Swans at Coole," the speaker counts the swans on the water and reflects that this is something he first did nineteen years ago. He does not reveal how many swans there were then, or whether these are the same swans, but it is clear that not much has changed in the landscape, the lake, or the swans themselves. Their hearts, the speaker says, "have not grown old," and the obvious contrast is with his own heart, which he describes as "sore" immediately before he remarks,
All's changed since I, hearing at twilight,
The first time on this shore,
The bell-beat of their wings above my head,
Trod with a lighter tread.
The speaker was younger and more carefree when he first saw and counted the wild swans at Coole. His step was lighter, he tells the reader, and so was his heart. He contrasts the changes in himself with the constancy of the landscape, which only makes his own degeneration more obvious by contrast.
Coole Park was the home of Lady Gregory, a member of the Anglo-Irish aristocracy and a leading figure in the Irish Literary Revival. Yeats admired families such as the Gregorys and estates like Coole, since for him they represented permanence in a world that was changing fast. In this poem, it is the speaker who has changed for the worse, and the timeless environment of Coole accentuates this.