I usually say half full but that is just how I describe it. For instance, it would make more sense to say “that glass is half full of soda” and “that glass is half full of coffee” than it would be to say “that glass is half empty” because half empty is less specific. It is easier to describe what is there than what is not unless you want to not be specific in what is there.
I do not attribute any other belief to it other than the fact that it is half full of contents.
I try to react towards other situations in my life the same way, accepting what is as fact and dealing with it as it is.
I try to be a realist. I lean towards pessimism but yank myself out of it when I catch myself and deal with the facts.