While the possibility for life is hugely likely, given the immense time and enormous quantity of planets, the evolution of intelligence is another matter. That requires even greater overcoming of limitations. Intelligence requires sophisticated cells. There are immensely unlikely events on a par with that of the formation and incorporation of DNA.
On this planet the incorporation of DNA took place early on when the Earth had cooled and conditions were right. The formation of Eukaryotic cells (sophisticated cells that would support complex multi-celled life) requires two incredible occurrences. Firstly they have to incorporate or evolve cellular powerhouses to provide energy. On Earth this happened when bacteria (that were mitochondria-like) became symbiotically incorporated into cells. Secondly they have to have incorporated chlorophyll-rich chloroplasts to break down water to release oxygen and produce food.
The plants incorporated chlorophyll rich bacteria symbiotically. In so doing they changed the atmosphere of the planet and the oxygen enabled life to become more complex.
These two limiting factors are incredibly difficult leaps.
Not only do planets have to be in the ‘Goldilocks Zone’ and have given rise to life that incorporates DNA (or its equivalent) but it would also have to evolve through these two other immensely difficult bottle-necks in order to achieve the complexity necessary for intelligence.
The consensus is that this will only occur on an incredibly small number of occasions.
Fortunately with the billions of planets on which life will have occurred this still means that there are likely to be hundreds of thousands of planets out there supporting intelligent life.
There is intelligence out there! How do we contact it?