What we consider to technically be life is probably common throughout the universe. But Complex Life Forms are probably rare and perhaps even unique to Earth itself. If you ever get the chance, read the book "Rare Earth". Its written by an Astronomer and a Geologist. Once you read this, you'll have a new understanding of just how amazing it is that complex life on earth even exists.
It talks about of course how important the atmosphere and position of the earth to the sun is. But it also talks about other vital things such as the MOON! YEP, without the moon, and its effects on the Earth, complex life would not be possible. There would be no seasons and the axis of the earth would be tilted in such a way that one of the poles would constantly be facing the sun while the rest of the planet would be deprived or devoid of sunlight. How was Earth's Moon formed? Another planet collided with the Earth early in the history of the Solar System. How often does that happen with an Earth-Moon system that we have being the result? Another thing is that the Moon very slowly gets farther away from the earth as time passes. If the situation were reversed, the Moon would eventually collide with the earth producing a situation that would indeed wipe out complex life forms.
Jupiter and the other planets with their orbits are vital in stabilizing the Solar System and helping to attract and remove rocks and debris that could wipe out complex life on earth. The orbits of nearly all planets that have been found in other Solar Systems are eliptical instead of circular. All it takes is one planet with an eliptical orbit to create conditions that could prevent the development of complex life forms in the Solar System.
The Galaxy that the Earth is in is also ideal as well as the Sun and Earths position in that Galaxy. Were positioned far from the center where conditions tend to be chaotic, but far from the outer regions where the elements are to light to form the type of stars and planets needed for complex lifeforms.
After reading this book, I still think its possible that ET is out there, but because ET is so rare and the Universe is so vast, Humans are unlikely to ever ecounter ET.