O que significa "There either is or is not"?

“There either is or is not, that’s the way things are. The colour of the day. The way it felt to be a child. The saltwater on your sunburnt legs. Sometimes the water is yellow, sometimes it’s red. But what colour it may be in memory, depends on the day. I’m not going to tell you the story the way it happened. I’m going to tell it the way I remember it.

— Great Expectations (1998)


Estou com problemas em relação a expressão "There either is or is not", se alguém poder me ajudar desde já agradeço.