The Unsustainableness of Life

A friend of mine once told me that life is a lot like building a sand castle on the beach. All of a sudden the tide comes in and the waves just crash over it and destroy it. And even the very structures we build will be eventually destroyed or torn down. I don't know if those things really will last forever. They might last for thousands and thousands of years, but there is a futility to all that we do.