The hubble deep field is really just a small glimpse into space right?

It;s like looking through a keyhole we looked at a portion of space for 10 days and found a bunch of galaxies bu isn't;t that just a glimpse of space how can astronomers claim to know it all? The big bang looking back at the birth of the universe all this seem like bs to me do you agree? It's like taking a pair of binoculars and looking out to sea and saying i know everything!