Human knowledge isn't endless, but human belief is.

Humans have a tendency to discuss ideas which they'll never quite understand or be sure of.  Often these are things which humans will never quite understand, like the creation of the universe.  I think that this limits human knowledge, because something is only knowledge if it is the collective belief of people, which it seldom is.  I also think that human knowledge can never be endless because there are a finite number of things to know (or at least that we can know).