I'm thinking I've heard of it referred to as the idea that any aliens around right now would either be ascended or amoeba. That is to say, they would be highly technologically advanced, or would be simple organisms.
Think of it like randomly putting dots or short lines on a mile long piece of paper - it's unlikely that any of them will overlap. Since we assume that it takes approximately 10,000 years for a civilization to become trans-newtonian (again, not based on the fermi anything, because that's irrelevant in a universe where we -have- found ET life, but based on the fact that the default start date in aurora is 2025 or w/e it is, and thus it would have taken humans that long), it spends only 10,000 years in a state of non-trans-newtonian civilization. That's 10,000 years in the 14 billion year history of the universe, or even just the 4 billion year history of the planet. If there was another planet created at the same time as earth, exactly like earth, there's no reason to think that it would have gained intelligence at the same time as us. If it had taken just 12,000 years longer to get there, we wouldn't be seeing it as a pre-trans-newtonian civilisation in aurora until the year 4000 or so. And much longer if we assume the pre-trans-newtonian race needs at least city-level technology. Whilst 12,000 years might seem like a long time to you, remember that the life on both planets has already been evolving for 4 billion years (4,000,000,000 years, to put it in perspective). For it to take an additional 12,000 is nothing.
Another way - if you had a program instructed to randomly generate a "special" point or 10,000 with a probability of it happening once every 4 billion points, it's unlikely that if you ran even a large number of the program, you would end up with any of the simulations overlapping the points with each other.
Although as I say, I didn't do that math, I don't know how many it would take to make it probable, or how many life-bearing planets there are.