It's improbable to think that our Earth is the only life-sustaining planet in all of the galaxies, and even the entire universe. If there are humans on one planet, there can be life on another planet. But it doesn't have to necessarily be humans. Like if there is life on Pluto, it can be microscopic, but it's still life sustaining !
The amount of potentially habitable exoplanets found in such a small region, as compared to the size of the Universe, recently makes it highly probable that there is a large amount of intelligent species residing in the universe.
I don't feel 100% confident that there IS intelligent life elsewhere in the universe, seeing as you know, we've never detected any. But given the sheer, mind-boggling size of this universe and just how much we DON'T know about it, there easily could be.
We do not know for sure, but look at the Earth compared to the universe. We are one spec of dust. Now, look at the universe in the scale of the potential multiverse. For life to only be on one insignificant speck of dust sounds preposterous. There almost certainly is life out there, but whether it is intelligent, or if we recognize it as intelligent, that is something that we can not know at this point.
even with the incredibly small odds for there being life out there at all, ths infinitely large size of the universe only makes it a guarantee that theyre out there.