The Size of Infinity

 I'm confused; that's the short version of this post, I think. In class, we discussed the ways in which we might compare the sizes of different infinities - whether one infinity could contain more than another. When the argument is put forth, I feel that I understand it, yet when I try to explain it to myself, I fall short. The Library of Babel contains infinite possibilities, yet there are an untold number of possibilities even greater still? I almost comprehend this, I think, but not quite... I'm confused. Really confused. If the existing possibilities are never-ending, how then can even more possibilities exist? And why would we care? We're never going to exhaust the contents of the Library of Babel; what does it matter if, theoretically, there are even more possibilities beyond it? I suspect that the metaphor has become muddled in my mind.