The observable universe was already incomprehensibly big, but it now looks to be even bigger. Astronomers have determined that are likely about 10 times more galaxies than previously thought, or between 1 trillion to 2 trillion. We just don't have the technology (or physical proximity) to detect them all, according to the researchers. They reached the conclusion after converting Hubble Deep Field images into 3D to study the number of galaxies at a given point in the universe's history, and using mathematical models to infer the possibility of galaxies that we haven't spotted. Simply speaking, the volume of galaxies seen over time doesn't make sense unless there are many we aren't aware of.
Why don't we see them? It may be a combination of our limited technology with the evolution of the universe itself. We can only do so much to account for redshifting (the light effect as objects move further away) and interference like cosmic gas, and that's before accounting for the ever-changing nature of the cosmos. At least the data may help answer a key riddle. The shrinking number of galaxies supports the theory that galactic mergers are shaping the universe, radically reducing the overall galaxy count as more and more collisions take place.
It could be a long while before it's possible to directly verify these calculations. There may need to be a dramatic improvement in telescope technology. And remember, even the 2 trillion figure likely doesn't represent the whole universe. The very nature of light limits our ability to see the whole of existence -- it's possible that there are many, many more galaxies lurking out of range.