[UncleOxidant]

Maybe intelligent life isn't so rare, but technologically advanced intelligent life is exceedingly rare? It's possible that there could be planets where life emerged, evolved to an intelligent species that didn't have to compete for resources, maybe there were no large carnivores to worry about, maybe resources are even less scarce than they are here, maybe they developed a very collective culture and thus no concept of war, whatever - some scenario where technology doesn't really develop very far. It would never occur to this species to want to leave their planet to go exploring. They could be quite content to live this way for millions of years. We'd never see any signals from them.

When it comes to questions like the one posed in the fermi paradox we always seem to assume that all intelligent lifeforms would be very much like us with similar drives and culture. But it seems exceedingly unlikely.