All things have a beginning, all things have an end.
Simple. Pithy. And, true. Nothing lasts forever, not even the universe. (in theory) So, enjoy the journey while you can.
To quote Patric Stewart's character Picard - "Someone once told me that time was a predator that stalked us all our lives. I rather believe that time is a companion who goes with us on the journey and reminds us to cherish every moment, because it will never come again. What we leave behind is not as important as how we've lived. After all Number One, we're only mortal."