Is the glass half FULL or half EMPTY?

There are 2 very thirsty people, in need of water. The first arrives in front of a glass of water and begins complaining, "this glass is half EMPTY!!!" A minute later the second person arrives in the same place and says, "this glass is half FULL!"

One moment later, the second person drinks the water. The first person complains, "Now the glass is TOTALLY EMPTY!!! Why did you drink it!?" The second person doesn't hear the complaining though, because they are already far away searching for more water.