Tiffany's speaker sits alone in a room and watches the year turn: flowers blooming, snow falling, leaves piling up and dying. Each season gets its own small image. Snow is both "a gift" and "a curse," and the dying leaves are compared to an old person slowly fading. Summer is the one the speaker loves, though it comes with a cost, because summer means being around people.
That's where the poem turns personal. The speaker says others can't see a "dark soul" or "dead heart" and only notice someone who seems happy. Nobody asks whether that happiness is real, and they simply go along with it, like leaves blowing in the wind. The mood is quiet, lonely and a little sad, though the nature descriptions are tender. In the last lines the speaker notices they have compared nature to people, then insists nature is far more beautiful than humanity could ever be. It reads like a confession wrapped in weather.