You cannot step into the same stream twice.
A clay cup sits in front of you.
How does its function change when it is full versus when it is empty? A full cup is useful in that you can drink from it; you can use the resources inside it. But what use does an empty cup have? You cannot drink from it, so how can it be useful? Which would the optimist—or the pessimist—choose? Is it better to be half empty or half full?
Conversely, what if you wish to add more liquid to the vessel? Would you want it to be empty or full? What is the function of the liquid then? Its value?
Take these questions in for a moment. Chew them, taste them, savor them.
What is that cup? The vessel, ...