On a basic level, Breakfast at Tiffany's is about looking forward to the future and about the dreams, hopes, and plans we make for ourselves. In many ways these dreams sustain the characters, as they are propelled by the promise of something better than what the present can provide. But when these same hopes, and plans are shattered, this has devastating effects on the dreamers. Suddenly, they have to revise what they've been looking forward to, and this throws some characters into a tailspin as they're suddenly forced to reevaluate their lives.
The dreams and plans the characters have are pipe dreams. They'll never actually see these aspirations come to be.
None of the characters actually have any plans. They just float through life waiting to see what happens.