Given the proper conditions, life might form once in a thousand planets, and intelligent life might be one in a billion. We don't know, but there's some probability for both. It could be really low, or it could be relatively high.
The Rare Earth solution to the Fermi Paradox is as good a guess as any. Life of some kind might be relatively common, but intelligent life could still be really rare. We are the only species on Earth in 3.5 billion years to make radio telescopes and spacecraft.
On other worlds, it might never happen because of the thousand different factors that led to hominid evolution which might be different elsewhere. For example, If the non-avian dinosaurs hadn't gone extinct from a large meteor impact, who knows whether any technological civilization would have ever formed. At any rate, mammalian evolution would have gone differently, and it's anyone's guess whether some non-hominid intelligent species would have evolved instead. They didn't during the age of the dinosaurs.
We don't even know whether multicellular life is a low probability event. Maybe Cambrian explosions don't happen very often.
There's no inevitability here, only unknown probabilities.
