Life is nothing more than a series of changes. Life evolves this way. Nothing remains unchanged, not even our oceans, our mountains. Things come and go. People come and go. And when they go, you say goodbye.
Sometimes you don't even realize they go, they are just gone when you raise your head and look around. Did they leave something behind or is it just the smoke of their cigarette still lingering in the air?
It's relieving to say goodybe in the way that you can still leave something behind or give something in return for the moments of your life that you have passed together. It's important to give and not just to take.
And then, it might even turn out that the goodbye was just a hello.