The pessimist sees a glass half empty; the optimist, a glass half full. Someone who can see, however, sees 4 ounces of water, and a method of storing that water, of containing and giving form to that water, without comment.
Water is present, and there is little need to measure air. The size of glass itself is irrelevant, to the extent that it is sufficiently large to accomplish its storage task. An aquifer might be 90% empty, but able to provide for a city.
It is my own species of “optimism” to try and reliably see what recources ARE available. It is little use to imagine the endless infinity of things which are NOT present before us. Rather, an acceptable use of imagination is to see the endless things which can be done with what we have.