Why haven't we found any evidence of Extra-terrestrial life? (Fermi paradox)?

First of all, I don't want answers about any government-UFO cover ups. I mostly want to see the "Fermi Paradox" addressed. I'm a little confused as to what is the most acceptable to this paradox. Is it because civilizations eventually destroy themselves? or because of advanced technology (such as digital frequencies) that make them hard to detect? or is the chance of life occurring just simply impossible? Is there any other reasons that could be behind this paradox?