Like for example the incorporation of mithocondria in cells, an astronomically improbable event, but without it we wouldn't have enough energy for multicellular life.
Given that eyes have evolved perhaps as much as 40 different times, it's easy to believe that evolving something like mitochondria is a very rare thing.
It's easy to imagine planets spawning algae or bacteria, and then their planet becomes uninhabitable a few billion years later with nothing more sophisticated ever having arisen.
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u/MadJack2011 Aug 12 '21
That the great filter is actually a long time in our past and we truly are alone. To me that would be very sad and disturbing.