The Great Filter is the idea that, in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.
https://en.wikipedia.org/wiki/Great_Filter
The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now."
https://en.wikipedia.org/wiki/Fermi_paradox
Personally I think it's photosynthesis. Life itself developed and spread but photosynthesis started an inevitable chain of ever-greater and more-efficient life. I think a random chain of mutations that turns carbon-based proto-life into something that can harvest light energy is wildly unlikely, even after the wildly unlikely event of life beginning in the first place.
I have no data to back that up, just a guess.
Everyone is talking about society or physiology stuff. That is just things that might get humans.
Stars going super-nova is the real great filter. Our sun is 4.6 billion years old. Life started 4 billion years ago. In 4 billion years, the sun goes supernova. We are halfway to the end of the earth.
Smaller stars last longer, but have smaller ranges that life can exist in - and planets tend to move in or out in their orbits. Bigger stars have giant habitable zones - but some large stars born when humans took their first steps are in their last decades of life. You couldn't get from the pyramids to NASA in that time, never mind the 4 billion years it took to get to humans.
I think it's supposed to actually less than that, the sun's luminescence will increase over the next 1 billion years to the point that it will boil off the earth's oceans. No life will be able to exist past that, and earth will just be a barren rock in orbit for the next 3 billion years.
Well I'm doing my part to make sure the oceans are full of Arctic ice for the great boil off
When they do boil off they need to make sure to have a hell of a lot of cocktail sauce and melted butter on hand.