If there is life elsewhere in the universe, then why haven't we seen it yet?

This simple question has come to be known as "The Fermi Paradox" and many scientists have struggled to find a suitable answer. In order for us to have an informed discussion about the topic, read this excellent article Links to an external site., which presents six possible explanations of why we haven't found irrefutable evidence of life in the universe yet.

Choose the one proposed solution that seems the most convincing to you. Explain why you think this is the best explanation.