I've pondered this from the perspective of the Fermi Paradox; that Earth had a really fortuitous series of events where the planet went down one line of flora/f

I've pondered this from the perspective of the Fermi Paradox; that Earth had a really fortuitous series of events where the planet went down one line of flora/fauna evolution that, despite millions of years of evolution didn't to our knowledge amount to intelligent life; experienced a global apocalypse which allowed that (plus later/earlier) flora/fauna to decay and become an easily available source of energy; then had a second line of evolution which did, for whatever reason, result in intelligent life; which now has access to all that energy from the last iteration. To me, that's a really convincing explanation for the Fermi Paradox. There may be other intelligent species out there, but evolution on earth seems to have a history of producing killing machines (and crabs. its always crabs). So, the gate to get to intelligent life isn't probable; and then you hit the gate of "does that intelligent life have enough local resources to escape the gravity well of its own planet", a gate which for earth practically required a prior chain of hundreds of millions of years of evolution, and an opportune asteroid impact to clear that chain out and make way for a new one to roll the dice again. The mitigating factor for the second gate is: There could be other resources which could provide the power to escape a gravity well independent of biological decay (e.g. uranium, hydrogen). But at least in human history: think of what it took for us to fully understand how to harness oil, let alone uranium or hydrogen, create a rocket, and get to space safely; we did that with the tremendous benefit of plentiful hydrocarbon resources (global shipping, computers, mining rigs, plastic, etc). At minimum; a species without this advantage would take a lot longer to get to our level; but we did it in just a couple hundred years. Universal timescales help, but they also work against; as the earth has showcased, planets get bombarded by civilization-ending asteroids often. So, either an element of luck, or: a species has to have these structural advantages, and apply them for the purposes of asteroid defense before the next one hits; or its all over and the clock resets. Point being if I were a betting man: there are probably between 1 to 4 civilizations in our galaxy (including us) which have reached a similar or greater level of technology; but a great number more that are functionally trapped in a steampunk age, unable to escape their own planets. My other more fringe theory for the Fermi Paradox, which to be fair is practically the entire plot of The Last of Us, is: that the Apex Predator on every planet that is capable of evolving carbon-based life is Fungus. Eventually, Fungus always wins; and takes intelligent civilization with it.